Ančić helped Croatia to win the 2005 Davis Cup and claimed a bronze medal for the country at the 2004 Athens Olympics, in men's doubles partnering Ivan Ljubičić.

As a teenager making his major debut at the 2002 Wimbledon Championships, he defeated seventh-seeded Roger Federer.

During 2007 and 2008, infectious mononucleosis and minor injuries forced him to miss many major events, and his ranking dropped from No.

[citation needed] His ATP debut was at Miami Masters, where he drew a wild card, but he lost in the opening round.

[12] The highlight of his Grand Slam debut at the 2002 Wimbledon Championships was the major upset of his first round defeat of Roger Federer, the seventh seed, 6–3, 7–6(2), 6–3 in just under two hours.

His 2005 highlights also include the final at the Japan Open Tennis Championships, losing to Wesley Moodie.

[citation needed] Ančić started on the 2006 ATP Tour with strong note in his second tournament of the year in Auckland, where he defeated top seed Fernando González on his way to the final.

Ančić was defeated by David Nalbandian at Miami and Rome and by Roger Federer at the French Open and Wimbledon.

Ančić missed the U.S. hard-court season due to a knee injury received in a jet skiing accident.

In September, in the first event after the summer injuries, he reached the final at the China Open, losing to Marcos Baghdatis.

[18] Later, he confessed that he was playing sick a week before in a match against Germany in the Davis Cup, and the virus had started to affect him at the Australian Open.

Ančić fractured a small bone at the gym a week before the US Open, which was the third Grand Slam he missed in 2007.

[6] Ančić started the 2008 season again with illness and was forced to withdraw from the tournaments in Australia, missing his fourth Grand Slam in a row.

After a good start at the beginning of the 2009 season, Ančić announced in May that he would pull out of the French Open, Wimbledon, and the Davis Cup semifinal match, again because recurrence of mononucleosis.

[24][25] Ančić returned to the main tour level at the 2010 BNP Paribas Open, where he made it to the third round.