Top-seeded Andy Murray lost a set for the first time in three tournaments on Wednesday, but still had enough to defeat Slovakia's Martin Klizan 6-3, 6-7 (5), 6-0 in the first round of the Erste Bank Open in Vienna, Austria.
Murray had not dropped a set in his previous 11 matches before the second-ranked Scot struggled at times during the second set. He held leads of 4-3 and 6-5, but Klizan broke serve twice to force the tiebreak.
Murray dominated the final set, conceding two points on his own serve and 27 of 35 points overall.
Karlovic came back from a 5-1 deficit in the final set to knock off Damir Dzumbhur of Bosnia-Herzegovina 7-6 (6), 4-6, 7-6 (5).
Isner advanced by recording 31 aces in a 7-6 (1), 3-6, 7-6 (2) victory over Spain's Feliciano Lopez.
In other first-round matches, Germany's Phillipp Kohlschreiber beat Stephane Robert of France, 4-6, 6-3, 7-6 (3), while Spain's Albert Ramos-Vinolas rolled past Italy's Fabio Fognini, 6-2, 6-2.