At the request of his father, Ryoma Echizen moves to Japan after having success at tennis in the United States, having won four consecutive American Junior Openings. On his way to a Japanese tennis tournament, he "saves" Sakuno Ryuzaki from some thugs. Due to this, he misses the tournament, however, he finds an opponent in the form of one of the thugs he met on the subway. He then puts his opponent, Sasabe, in his place during the match, where he reveals his exceptional tennis capabilities.
Upon his arrival in Seishun Academy, "Seigaku" for short, Ryoma teaches a lesson to two juniors who are picking on the freshmen. Takeshi Momoshiro, one of the team's regulars, puts a stop to it and decides to play Ryoma in a tennis match. Noticing that Momoshiro has a bad ankle, Ryoma decides not to play with his dominant hand. Also, Sakuno's energetic friend, Tomoka, is introduced to Ryoma, and instantly proclaims herself to be his number one fan.
The Seigaku regulars are introduced, while a journalist, Mamoru Inoue, and a photographer, Saori Shiba, visit Seigaku in order to report on the team's upcoming ranking matches. Meanwhile, Ryoma defeats a second year non-regular, Arai, using an old broken tennis racket when the latter hides all three of Ryoma's rackets. Seeing his skill, the captain of the tennis team, Kunimitsu Tezuka, enters Ryoma's name on the roster for the intraschool ranking matches despite the fact that he is a freshman.
The Seigaku ranking matches has begun, and Ryoma and the Seigaku regulars continue to win their matches early on in the tournament. Ryoma then gets pitted against regular Kaoru Kaido in the third round, where the latter reveals his special move, the Snake shot. This throws Ryoma off guard, so he decides to switch to his dominant hand.
Kaido attempts to use his Snake shot to wear off Ryoma's stamina, and though Ryoma initially shows signs of sweating and fatigue, he surprises both Kaido and the spectators when his speed and power does not decrease. Near the end, it is revealed that Ryoma had been implementing a plan: he had been specifically hitting shots that Kaido had to bend his knees in order to return, thus Kaido would loose stamina far faster than Ryoma. His plan works, earning him the win.
Inoue plays a match with Nanjiro Echizen, the former "Samurai Nanjiro", a legendary tennis professional, to get answers about why he retired. Though Nanjiro appears to not be taking it seriously, his skills show otherwise, and he easily beats Inoue with both his eyes closed. However, Inoue finds out that Nanjiro is now focusing on developing the skills of his son, Ryoma. Meanwhile, Sakuno looks for Ryoma to learn more about him and tennis.
In Ryoma's next ranking match, he plays against Inui Sadaharu, who uses Data Tennis to counter Ryoma's play style. Using the data he gathered from Ryoma's previous match, Inui is able to dominate the match by accurately predicting and countering Ryoma's moves. Though irritated, Ryoma refuses to give up and reveals that he is glad to have transferred into Seigaku because he can now play against different types of players, like Inui.
In order to counter Inui's data, Ryoma uses a new technique he had practiced when playing against his father, the One-footed Split Step. This requires him to continuously hop in place so he can react faster to the ball, as well as be able to move to another part of the court more quickly. Using this technique, Ryoma gains enough agility and speed to return Inui's calculated shots. This, along with the Twist Serve, surpasses Inui's data and turns the game into Ryoma's favor.
Inui continues to be unable to return Ryoma's Twist Serve, resulting in his eventual loss. Ryoma then wins his next games, and finally becomes a regular. Meanwhile, Inui plays against his next opponent, Kaido, who also surpasses Inui's data and takes a spot in the regulars as well. With eight spots taken, Inui loses his place as a regular, however, Seigaku's coach, Sumire Ryuzaki, asks him to help in the regulars' training instead. During training, he introduces his special and dreaded vegetable juice, which most of the regulars fall victim to.
Ryoma and the rest of the freshmen go to where Kachiro's father works as a tennis coach. However, they find trouble with Sasabe again, but this time, Sasabe's father is the bigger problem. In order to teach him a lesson, Ryoma asks the father to teach him tennis. Though Sasabe warns his father not to, the latter is more than willing to do so. In their practice match, the father ends up pulling a muscle after Ryoma shows him just how much he should have listened to Kachiro's father's advice about warming up first.
Realizing that the only remaining singles slot left is singles 3, Ryoma and Momoshiro compete for it when they both want to play singles in the upcoming match against Gyokurin Middle School. However, when they decide to settle it with a match, they end up playing doubles against locals instead. Though they defeat their first few challengers, they are utterly defeated by two cocky Gyokurin players due to their lack of teamwork. It is then that the two decide to play doubles in the upcoming match.
Momoshiro and Ryoma volunteer to play in doubles 2, and develop a tactic to improve their playing coordination. However, despite their practice, they continue to clash with each other due to their natural dominant tendencies as singles players. In addition, their rivals use a strategy which takes advantage of Momoshiro and Ryoma's lack of coordination, turning the game into their favor.
With their new strategy, Gyokurin continues to dominate. Irritated, Ryoma and Momoshiro realize that they are truly not suited to be doubles players, and agree to split the court in half. Now they each only have to defend one half of the court and is able to utilize their individual skills. Though strange, it is an effective strategy that wins them the game. However, due to their shameful performance, they still receive punishment from their coach.
Fudomine Middle School, an unknown team that withdrew from last tournament for internal affairs, is Seigaku's next rival. In the first game, Seigaku's Shusuke Fuji and Takashi Kawamura find themselves struggling against the first Fudomine pair, forcing Fuji to use one of his Triple Counters, Tsubame Gaeshi, a technique that causes the ball to roll rather than bounce once it reaches the opponents' side of the court.
Determined to overcome Fuji's skills, Fudomine's Tetsu Ishida tries a desperate measure to seal Fuji's Tsubame Gaeshi by using a hit of considerable strength called Hadokyu. When he aims it directly toward Fuji, Kawamura decides to get in its way when he realizes that Fuji would not be able to return it. Hoverer, though he succeeds in returning it, he hurts his wrist in the process, forcing Seigaku to forfeit the match.
Thanks to Eiji Kikumaru's acrobatics and Shuichiro Oishi's ability to adapt to his partner's style, Seigaku's "Golden Pair" wins their doubles match easily. Next is the game between Kaido and Kamio Akira, where Kaoru's Snake shot turns out to be ineffective against the speed ace from Fudomine. In a moment of desperation, Kaido inadvertently performs a near impossible shot around the net's pole, which is then dubbed the Boomerang Snake.
Kaido desperately tries to recreate the Boomerang Snake, but he eventually stops his attempts when he decides to just play his style of tennis. With neither side yielding, Kamio's and Kaido's game becomes an endurance match. However, in the end, Kaido's willpower and persistence outlasts Kamio's stamina. Also, Momoshiro learns the identity of the girl he has been recently running into, who turns out to be Fudomine's player-coach and Kippei Tachibana's younger sister, An Tachibana.
Nanjiro Echizen finds a letter from Ryuzaki and remembers the days when he trained under her as a Seigaku regular. Meanwhile, Ryoma's opponent, Shinji Ibu, shows his skills when he is able to return Ryoma's Twist Serve, as well as his revealing his own serve, the Kick Serve, which is similar to the Twist Serve. Ryoma then switches to his left hand, and the game heats up between the two player's serves.
Ryoma struggles to resist Ibu's "spot", a technique where Ibu forces Ryoma to hit certain shots that temporarily paralyzes his arm. However, when Ryoma tries to avoid the spot by continuously switching his racket from his left and right hands, the racket gets loose from his grip and it bounces back, hitting his eye. With his eyelid bleeding, it seems impossible for him to continue, but he insists on continuing the match.
Impressed with his determination, Tezuka gives Ryoma ten minutes to finish the game, after which he will forfeit the match. In the end, Ryoma manages to overcome Ibu's "spot" and wins the match right before his alloted time had ended. With Ryoma's win, Seigaku wins the tournament, and after tending to his wounds, the Seigaku regulars celebrate in Kawamura's sushi restaurant.
Due to their recent victories, spies from other schools begin to observe Seigaku's training. When they catch two of the spies spying on them even after school hours, Momoshiro and Ryoma teach the two of them a lesson in a doubles match. When the two spies are only able to score one point against them, they decide to practice their tennis, instead of spying on others.
While Kaido starts his daily training, Momoshiro and Kamio Akira end up playing a doubles match against two Hyotei regulars, Atobe Keigo and Munehiro Kabaji, when the latter two pick on An Tachibana. Meanwhile, Ryoma and Shinji Ibu battle over grip tape by creating a contest in which they catch a pickpocket. Kaido is then unwittingly dragged into the mess when he is suspected of being the thief.
During their new training regimen, Kaido and Oishi are forced to drink Inui's special vegetable juice for losing in their training match, becoming very sick. Then, when Tezuka accidentally drinks all of Inui's juice, Inui is forced to use his "Golden Power Remix Inui Juice" on the loser of the Kikumaru and Ryoma match. When Ryoma fails to win the game within five shots, which was the requirement for him to win, he ends being the one to drink it.
Ryoma is asked by coach Ryuzaki to go to the racket-stringer with Sakuno, whom he constantly ignores, though unknowingly. Curious what Ryoma is up to, Nanjiro decides to follow him, and after seeing the two together, Momoshiro and the freshman trio, spy on the two, believing that that they are on a date. However, Ryoma continues to ignore her and even end up hurting her feelings when she asks about him. In the end, Ryoma tries to make up for it by teaching her some tennis.
Feeling that Ryoma's tennis is a simple copy of his father's, Tezuka asks coach Ryuzaki for permission to play an unofficial match against Ryoma. Before his match, Tezuka and Oishi go to a clinic to check whether or not Tezuka's arm has healed. Though it is healed, the doctor warns him not to play long matches and to not use his drop shot. After finding out he is fine, he meets up with Ryoma. Suspicious of the two's meeting, Oishi decides to follow the pair to see what is really going on.
During their match, in order to convince the latter to aim higher with his own style of tennis, Tezuka risks his re-injuring his arm by going all out in the match, resulting in Ryoma's defeat. Oishi, who was the sole spectator of the Tezuka and Ryoma match, talks to Tezuka about the outcome and its repercussions. The next day at school, the other team members, grow suspicious when Tezuka and Ryoma fail to appear during team practice two days in a row. Meanwhile, Ryoma asks Nanjiro for a match, in which the latter realizes that Ryoma has changed and will now get stronger.