Federer battles past Kohlschreiber

Roger Federer was made to work hard for his 6-4 4-6 6-4 victory over Phillip Kohlschreiber at the Valencia Open on Thursday.

The match was tightly contested throughout, with the top-seeded Swiss taking the first set with a single break point in the fifth game before another solitary break point opportunity decided the second set in Kohlschreiber's favour.

The third set saw both players stay rock solid on serve once more before Federer again carved out a lone break point in the ninth game, clinching it to go 5-4 up before closing out the match on serve.

Elsewhere, fourth seed Kevin Anderson bowed out of the tournament after going down 6-2 7-6 (8-6) to American Donald Young.

It was only Young's second victory over a top-10 opponent of the season. He dominated the first set before narrowly edging a 70-minute second set in a close tie-break.

Young moves on to face countryman Jack Sock, who knocked out compatriot John Isner with a 7-6 (7-5) 6-3 victory, fending off 14 aces from the big-serving 30-year-old to advance.

Sock and Isner are friends off the court, which made the job even harder.

"Those matches are never fun, playing one of your best friends on the tour," said Sock. "It never sits to well after the match. It's part of the game. Somebody's got to win. He's done it to me a few times. Fortunately, today I was able to get through." 

Seventh seed Maric Cilic of Croatia set up a last eight meeting with Rafael Nadal by beating Teymuraz Gabashvili 6-3 6-1, while his countryman Ivo Karlovic maintained his run with a 7-6 (7-4) 7-5 victory over Dusan Lajovic.

Fifth-seeded Frenchman Richard Gasquet was the day's other winner, 7-6 (7-1) 6-4 over Dominic Thiem.