Karlović debuted for the Croatian Davis Cup team in 2000 against Ireland, where he won the dead rubber.
Karlović appeared in a starting line-up for the first time in 2002 against Argentina in Buenos Aires, but he lost to Juan Ignacio Chela in the second rubber and to Gastón Gaudio in the fifth and decisive rubber.
He has posted a 4–2 career record (2–2 in singles) in three ties since 2000.

Karlović caused a major upset at Wimbledon when he beat defending champion Lleyton Hewitt in his first match in a Grand Slam tournament.
As of 2015, Karlović remains the only player in Open tennis history, and only the second player after Charlie Pasarell, to defeat the defending Wimbledon men's singles champion in the first round.
He finished the 2003 year in the top 100 and as the Croatian No.
3, behind Ivan Ljubičić and Mario Ančić.
He also averaged an ATP-best of 17.6 aces per match.
He continued his success during the 2004 season, winning at Calabasas, California.
He reached the round of sixteen in several tournaments, including Wimbledon.
Karlović debuted for the Croatian Davis Cup team in 2000 against Ireland, where he won the dead rubber. Karlović appeared in a starting line-up for the first time in 2002 against Argentina in Buenos Aires, but he lost to Juan Ignacio Chela in the second rubber and to Gastón Gaudio in the fifth and decisive rubber. He has posted a 4–2 career record (2–2 in singles) in three ties since 2000.
Karlović caused a major upset at Wimbledon when he beat defending champion Lleyton Hewitt in his first match in a Grand Slam tournament. As of 2015, Karlović remains the only player in Open tennis history, and only the second player after Charlie Pasarell, to defeat the defending Wimbledon men's singles champion in the first round. He finished the 2003 year in the top 100 and as the Croatian No. 3, behind Ivan Ljubičić and Mario Ančić. He also averaged an ATP-best of 17.6 aces per match. He continued his success during the 2004 season, winning at Calabasas, California. He reached the round of sixteen in several tournaments, including Wimbledon.
Ivo Karlović