Updated

Andy Murray's return to the court after his U.S. Open triumph was a successful one, as the Scottish star claimed a straight-set win over Ivo Karlovic to start defense of his Japan Open title.

The top-seeded Murray earned a 7-6 (9-7), 6-4 victory Tuesday in his first competitive match since capturing his first Grand Slam title last month at Flushing Meadows with a stirring five-set win over Novak Djokovic.

His first scheduled opponent in Tokyo was by no means a pushover, and neither was his replacement. Gael Monfils was slated to face Murray, but the veteran Frenchman pulled out of the tournament with a knee injury and Karlovic took his place in the draw as a lucky loser.

The big-serving Croat blasted 17 aces and had Murray on the ropes in the first-set tiebreak. A double-fault cost Karlovic a chance for a 6-3 lead, but he still held a set point at 7-6. Murray, though, battled back and won the next three points to take the set, then broke Karlovic for the first time in the 10th game to win the match.

Next up for Murray, whose brilliant summer also included an Olympic gold medal in front of the home fans in London, will be Slovakia's Lukas Lacko in a second-round encounter on Wednesday.

A surprise on Tuesday saw Japanese wild card Tatsuma Ito pull off a stunning 7-6 (7-4), 7-6 (7-5) victory over fifth-seeded Nicolas Almagro of Spain.

Other first-round winners Tuesday included sixth-seeded Milos Raonic of Canada and eighth-seeded Kei Nishikori. Raonic toppled Czech veteran Radek Stepanek, 6-4, 6-4, while Nishikori rallied past fellow Japan native Go Soeda, 4-6, 6-2, 6-3.

Also Tuesday, Spain's Tommy Robredo dumped Finland's Jarkko Nieminen, 6-2, 6-4; Russian qualifier Dmitry Tursunov edged Australia's Bernard Tomic, 6-4, 7-5; Frenchman Jeremy Chardy knocked out Japanese wild card Yuichi Sugita, 6-1, 7-5; Cypriot Marcos Baghdatis eliminated Ukrainian qualifier Sergiy Stakhovsky, 7-6 (7-3), 7-5; Swiss qualifier Marco Chiudinelli battled past Slovakia's Martin Klizan, 7-6 (7-3), 6-2; and Colombia's Alejandro Falla notched a 7-5, 6-2 victory over Brazil's Thomaz Bellucci.

Two first-round matches are on Wednesday's schedule, as third-seeded Janko Tipsarevic takes on Frenchman Gilles Simon and fourth-seeded Juan Monaco meets Bulgarian qualifier Grigor Dmitrov. Monaco is coming off last week's win in Kuala Lumpur, his first title on a surface other than clay. Simon was the runner-up last week in Bangkok and beat Tipsarevic to reach the final.

The winner of this event will claim a first prize of $308,000.