Roy "Tin Cup" McAvoy (Kevin Costner) is a former golf prodigy leading a generally aimless existence. He owns a ramshackle driving range in West Texas, where he drinks and hangs out with his pal Romeo Posar (Cheech Marin) and their friends. One day Dr. Molly Griswold (Rene Russo), a clinical psychologist, arrives looking for a golf lesson. She has been dating David Simms (Don Johnson), a top professional golfer who played with Roy in college. Roy soon becomes attracted to Molly.
The next day David Simms shows up at Roy's trailer ahead of a local benefit tournament. Roy thinks he is being invited to play, but Simms actually wants to hire him as a caddie (since Roy knows the course). During the round, Roy needles Simms about laying up instead of having the nerve to take a 230-yard shot over a water hazard. A bet amongst the other players is made and Simms fires Roy after he makes the long shot.
To get even with Simms, Roy decides to try and qualify for the U.S. Open. He makes a play for Molly who is already his therapist.
In the first qualifying round, with Romeo as his caddie, Roy's game is excellent but his head needs help. Roy insists on playing recklessly and he demands the driver instead of the safe play which is laying up. Roy and Romeo fight and Romeo quits. Amazingly, Roy still manages to advance to the final qualifying round.
Without Romeo, Roy barely succeeds at the sectional qualifying round, earning a spot in the U.S. Open. Romeo returns and helps Roy with some swing problems.
On the first day of the U.S Open, Roy shoots a horrendous 83. Meanwhile, Molly sees Simms' unpleasant side and decides she truly wants to help Roy. With renewed confidence, McAvoy shocks the golf world by making the cut with an impressive score. Roy's third round is also excellent and it moves him into contention.
On the last day of the U.S. Open tournament, Roy is in a three-way battle to win. For the 4th day in a row, Roy takes a shot that repeatedly fails to keep the ball out of the water hazard. On his 12th and final shot, facing disqualification, he reaches the green and amazingly, it goes in the hole. Roy realizes that he has blown a shot at winning the U.S. Open, but Molly re-assures him about how people will always remember his amazing shot.
Back in Texas, Molly tells Roy that he automatically qualified for next year's Open due to his standing. They kiss passionately as the movie ends.
Kevin Costner as Roy "Tin Cup" McAvoy
Rene Russo as Dr. Molly Griswold
Don Johnson as David Simms
Cheech Marin as Romeo Posar
Rex Linn as Dewey
Linda Hart as Doreen
Dennis Burkley as Earl
Lou Myers as Clint
Richard Lineback as Curt
George Perez as Jose
Mickey Jones as Turk
Michael Milhoan as Boone
Jim Nantz as CBS announcer
Ken Venturi as CBS announcer