Isner survived tiebreaks in both sets to create a semifinal matchup with Lleyton Hewitt, the player he defeated in last year's championship match.
Isner eliminated Karlovic 7-6 (7-3), 7-6 (7-3). When those two meet, which they have done four times, they create the tallest tennis match in ATP Tour history. Isner stands 6-foot-9 and Karlovic is an inch taller. They have now split their four career matches.
Hewitt earned his spot in the semifinals by downing Jan Hernych 6-7 (6-4), 6-2. The only time Isner has defeated Hewitt in four career meetings came in this event a year ago. Hewitt defeated Isner this year at Indian Wells, Calif.