LONDON, Nov. 14 -- Roger Federer is one step closer to winning his seventh ATP Final championship after beating Alexander Zverev at London's O2 Arena on Tuesday.

Federer moved Zverev around the court with drop shots and slices and flatten out his groundstrokes against the 20-year-old right-hander, winning 7-6 (6), 5-7, 6-1 after two hours and 12 minutes.

The 36-year-old Swiss, who beat American Jack Sock in the group opener, thus guaranteed a place in the semifinals for the 14th time in his 15th appearance at the ATP Finals.

"I think I was able to stay the course and use my slice quite effectively, then try with variation to go into his forehand," Federer said.

"I'm extremely happy... It's been a tough group so to be there in two matches is great," Federer said. "But today was difficult. Still early days in the tournament. It was nice to be able to show maybe that quality of mine, that I can dig out these matches, these points time and time again, and stay mentally tough. In the third I started to play better. It was a tough match from the beginning till the end."

In the day's other match, eighth seed Sock upset fifth seed Marin Cilic of Croatia 5-7, 6-2, 7-6 (4) to move to 1-1 in Group Boris Becker. Sock also became the first American to win at the season finale since Andy Roddick 10 years ago today in Shanghai.

Cilic, who lost to Zverev in his first match, is eliminated. Sock and Zverev will fight for the other berth to qualify from the group.

Federer has now won 12 consecutive matches, dating back to his title runs at the Shanghai Masters and the Swiss Indoors Basel.

LONDON, Nov. 14 -- Roger Federer is one step closer to winning his seventh ATP Final championship after beating Alexander Zverev at London's O2 Arena on Tuesday.

Federer moved Zverev around the court with drop shots and slices and flatten out his groundstrokes against the 20-year-old right-hander, winning 7-6 (6), 5-7, 6-1 after two hours and 12 minutes.

The 36-year-old Swiss, who beat American Jack Sock in the group opener, thus guaranteed a place in the semifinals for the 14th time in his 15th appearance at the ATP Finals.

"I think I was able to stay the course and use my slice quite effectively, then try with variation to go into his forehand," Federer said.

"I'm extremely happy... It's been a tough group so to be there in two matches is great," Federer said. "But today was difficult. Still early days in the tournament. It was nice to be able to show maybe that quality of mine, that I can dig out these matches, these points time and time again, and stay mentally tough. In the third I started to play better. It was a tough match from the beginning till the end."

In the day's other match, eighth seed Sock upset fifth seed Marin Cilic of Croatia 5-7, 6-2, 7-6 (4) to move to 1-1 in Group Boris Becker. Sock also became the first American to win at the season finale since Andy Roddick 10 years ago today in Shanghai.

Cilic, who lost to Zverev in his first match, is eliminated. Sock and Zverev will fight for the other berth to qualify from the group.

Federer has now won 12 consecutive matches, dating back to his title runs at the Shanghai Masters and the Swiss Indoors Basel.