In 1996, he won the
NCAA singles championship as an
USC freshman, a feat that had not been achieved since
John McEnroe attended
Stanford University in 1978. Mamiit won the silver medal in the men's tournament at the
1999 Pan American Games in
Winnipeg, Manitoba, Canada, after losing the final to fellow
American Paul Goldstein. At the
2006 Asian Games held in
Doha,
Qatar, he won bronze in the singles event after losing in the semifinals to
Lee Hyung Taik of
South Korea. In the doubles event, he also won bronze, along with fellow
Filipino-American tennis player
Eric Taino, losing to the first-seeded and former
World no. 1 doubles players
Mahesh Bhupathi and
Leander Paes of
India. He won the men's singles in the
Ojai Tennis Tournament in 2008. His best tournament result came at the
1999 San Jose tournament. As a qualifier he defeated
Danish Kenneth Carlsen,
Americans Andre Agassi (although Agassi was up 6–0, 6–6 before he defaulted),
Australian
Mark Woodforde, and another American
Michael Chang before losing in the final to another Aussie
Mark Philippoussis 6–3, 6–2. Mamiit represented the
Philippines Davis Cup team, where he was undefeated until 2008. From January 2011, through the clay court season, he was the hitting partner for
Russian
Maria Sharapova, where she won the
2012 French Open to complete her Career Grand Slam. ==ATP career finals==