Australian Open champion Stan Wawrinka continued his quest for a fourth title this year by beating Marinko Matosevic of Australia 7-5, 6-3 to reach the semifinals of the grass-court Queen's Club tournament, a warm-up event for Wimbledon.

The top-seeded Wawrinka, who along with his victory at the Australian Open has also claimed titles in Chennai and Monte Carlo this season, will next play fourth-seeded Grigor Dimitrov. The Bulgarian advanced with a walkover when eighth-seeded opponent Alexandr Dolgopolov defaulted with a right thigh injury sustained in a second round doubles match late Thursday.

Spanish left-hander Feliciano Lopez held off a strong second set challenge to upset second-seeded Czech Tomas Berdych 6-4, 7-6 (7).

Wawrinka took time to gain the upper hand against Matosevic, who fought off three break points but then double-faulted at 6-5 to gift Wawrinka the only break of the first set.

Wawrinka then earned an early advantage in the second set, with a break to lead 2-0 deciding the outcome.

Tenth-seeded Lopez had to work hard for his victory, edging the opening set after breaking to lead 3-2 on his fifth break point.

In the second set, Berdych failed to convert a break point to lead 3-1 and then held three set points in the tiebreaker at 6-3 and another at 7-6 before double-faulting on his opponent's first match point.

"Very close, very close," Lopez said of the match.

Lopez next plays another Czech, Radek Stepanek, who rallied after dropping the first set to beat seventh-seeded South African Kevin Anderson 1-6, 6-3, 6-2.

Anderson fired seven aces and broke 15th-seeded Stepanek twice to take the opening set. But a break for 2-0 by Stepanek decided the second set, and two breaks in the third earned the Czech his first ATP Tour semifinal place since Memphis in February 2012.

"For a half hour I really had no chance. He hit every shot perfectly," said Stepanek.