SHANGHAI (Reuters) - U.S. Open champion Marin Cilic made a shock first-round exit from the Shanghai Masters on Monday after losing 7-5 2-6 7-6(2) to fellow Croatian Ivo Karlovic.
After dropping the first set, Cilic broke his opponent twice in the second to force a decider but Karlovic clinched the tie-breaker to seal victory in two hours and 16 minutes.
Cilic, sixth in the race to November's elite eight-player ATP Finals in London, had won his last two matches against Karlovic, who blasted 20 aces to his opponent's nine.
It proved a good day for big-servers as world number 14 John Isner belted down 22 aces to beat Spaniard Pablo Andujar 7-6(5) 1-6 6-3.
The American, who lost to Tomas Berdych in the China Open quarter-final last week, won 71 percent of his service points to win in just over two hours.
"Beijing was great last week," said Isner after his 38th win of the season. "I had a pretty good tournament. Got my tail kicked in the quarters. But I'm playing pretty well.
"I'm still alive here. I'm glad I'm not on a flight home tomorrow. It's all good. Playing better away from the States is something I'm always trying to do and I feel like it's something I've done so far."
Argentine Juan Monaco downed Portugal's Joao Sousa 6-2 7-6(4) to set up a second-round clash with eighth seed Milos Raonic.
Novak Djokovic, Rafa Nadal and Roger Federer are together this week in Shanghai for the first time since Wimbledon having already secured their places at the London season finale.
(Reporting by Amlan Chakraborty; Editing by Ed Osmond)