Stepanek won 6-7 (5), 7-6 (5), 7-6 (6), 6-7 (2), 16-14 in a match that lasted 5 hours, 59 minutes. The longest known Davis Cup match was 6 hours, 22 minutes between John McEnroe and Mats Wilander in 1982. The 82 games equaled the Davis Cup record since tiebreakers were introduced in 1989.
"I feel like I was in a 10-round boxing match," Karlovic said. "Everything hurts."
In the second singles Friday, Tomas Berdych beat U.S. Open quarterfinalist Marin Cilic 6-3, 6-3, 3-6, 4-6, 6-3 to put the Czechs on the verge of reaching the final for the first time since they won it in 1980.
Karlovic wasted four match points in the final set. Stepanek won when the 6-foot-10 Croat sent a smash wide. The were only five break-point chances in the match.
"I fought for my country," Stepanek said. "It was an amazing game."
This marathon equaled the number of games from a 1991 Americas Zone Group II match when Richard Ashby of Barbados beat Jose Medrano of Bolivia.
Karlovic obliterated both the men's record and Davis Cup record for aces - marks he held. He had 55 aces in a loss to Lleyton Hewitt at the French Open in May. His previous Davis Cup mark was 47 - also shared by Gustavo Kuerten and Marc Rosset - when he defeated James Blake at the World Group quarterfinals this year.
Croatia's Marin Cilic plays Tomas Berdych in the second singles Friday. The winner of the best-of-five series will face Spain or Israel in the final.
Croatia, the 2005 champion, has lost only once at home in its past 12 Davis Cup series. The Czechs, who won in 1980 when the nation competed as Czechoslovakia, are playing their first Davis Cup semifinal in 13 years.
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