Roger Federer lunges for a return to Alexander Zverev during their ATP World Tour Finals match in London on Tuesday. TONY O'BRIEN/ACTION IMAGES VIA REUTERS

Swiss ace shows he's still a cut above new breed

LONDON - Roger Federer kept upstart Alexander Zverev at bay in a gripping contest on Tuesday to reach the final four of the ATP Finals and stay on course for a seventh end-of-season crown.

The world No 2 saw off a spirited challenge from the much-hyped 20-year-old German 7-6 (6), 5-7, 6-1 in front of a boisterous pro-Federer crowd to become the first to reach the semifinals at O2 Arena.

"It was a good battle and I always enjoy myself at this beautiful arena," said Federer, who has now reached the penultimate stage 14 times.

"I have so much fun playing in London and I have been so successful here. Thank you for making it such a special night.

"I'm happy and relieved that I can play freely against Marin (Cilic), instead of it being a nailbiter. It's been a tough group, so to be through in two matches is great."

It evidently felt satisfying for Federer to beat one of the game's new comets. Asked if he could remember his first ATP Finals, he smiled: "It's so long ago I hardly recall it!"

Both players were scratchy on serve at the start of the match but quickly found their groove in a tight first set that saw no breaks of serve.

Zverev had to fend off two set points in the 12th game to force a tie-break.

The German third seed raced into a 4-0 advantage only to see the Swiss ace charge back to lead 5-4.

Zverev earned a set point of his own at 6-5 but could not convert and Federer made his third set point count.

The 19-time Grand Slam champion broke in the first game of the second set to establish an iron grip on the round-robin match, but Zverev rebounded in the fourth to get back on level terms.

Federer only landed 43 percent of first serves in the second set and it finally cost him in the 12th game, when Zverev capitalized on his third set point to force a decider.

Federer found his focus and some consistency on serve in the decider as Zverev's level dipped, earning three breaks to close it out 6-1.

Zverev has been touted as the leader of a pack of young guns hungry to oust the creaking old guard, but Federer, who has lost just four matches all year, shows no sign of capitulating.

Coming into the match, Federer, 36, and Zverev had faced each other four times and each had won twice.

This year, Federer beat the German in Halle but Zverev returned the favor at the Rogers Cup in Montreal.

Six-time Finals champion Federer may have been giving away 16 years to the youngster touted as the game's next major force, but he proved in a dominant third set that, at least for the time being, he remains a cut above his young pursuers.

The triumph in two hours and 11 minutes ensured the Swiss maestro booked a place in the last four for the 14th time in 15 appearances and with the tournament still only three days old.

It also meant that Zverev and Jack Sock will meet on Thursday to decide the other Boris Becker group qualifier.

Sock wins

Earlier, Sock kept his dreams of a fairytale finish to his season alive, beating Wimbledon finalist Cilic 5-7, 6-2, 7-6 (4).

"It's been an interesting morning so far," said the American.

"The fire alarm went off at 4 am and we had to exit the building. But I love playing here in London. It's an amazing atmosphere."

The top two players from each of the two groups of four progress to the semifinals.

Federer, who beat Sock in his first match, is the standout star at the tournament after the withdrawal through injury of world No 1 Rafael Nadal.

Novak Djokovic, Andy Murray and Stan Wawrinka are all long-term absentees from the Tour this season.

AP - Reuters