(Writes through with Sock win)
By Martyn Herman
LONDON, Nov 16 (Reuters) - Jack Sock became the first American to reach the last four of the ATP Finals for 10 years when he stunned world number three Alexander Zverev in a firecracker of a match on Thursday.
The world number nine, who barged through the back door to qualify for the London showpiece by winning the Paris Masters, won 6-4 1-6 6-4 to extend his season a little further.
Roger Federer had already won the Boris Becker group, having battled back to beat Marin Cilic earlier to post a perfect round-robin record at the event for a 10th time.
Six-times champion Federer won 6-7(5) 6-4 6-1 leaving the stage set for Zverev and Sock to slug it out for the runners-up spot and a semi-final against Bulgarian Grigor Dimitrov.
Talk of a possible Federer-Zverev re-match in Sunday’s final, after their high-quality duel on Tuesday, was doing the rounds but Sock, nicknamed ‘Showtime’, was not listening.
The 25-year-old from Kansas looked to have blown himself out when a 4-1 lead evaporated in the decider, but Zverev wobbled when serving at 4-5 and a double-fault followed by a forehand error handed Sock victory.
“That was a rollercoaster of a match for sure, that’s been the theme of my last few weeks, hang in there and keep fighting,” Sock, who seemed to be imploding when he received a penalty point at the start of the third set, said.
The American mixes eye-watering power with a deft touch and it was that combination that disrupted Zverev’s game.
Sock broke for a 4-3 lead in the first set and then almost gifted it straight back but recovered from 0-40 with five unanswered points to lead 5-3. Two games later a nonchalant drop shot gave him first blood.
Zverev roared back to take the second set in the blink of an eye although Sock carried on entertaining the crowd, as he has done all week, and at one point attempted a lob played through his legs rather than dispatch a routine forehand.
When Sock dropped serve at the start of the third he launched a ball into the upper tiers of the 02 arena.
The penalty point meant Zverev started the next game 15-0 ahead but the German lost concentration and conceded four straight points to get broken.
Zverev double-faulted to gift Sock another break for a 3-1 lead and was staring defeat in the face at 4-1 down.
He battled back but it proved in vain for the 20-year-old as a season, which earned him five titles, came to a sudden halt.
Federer had already booked a semi-final spot with his earlier win over Zverev but any notion that he would coast through his final group match proved wide of the mark.
Cilic was hoping to end his year on a high in the city where his Wimbledon dream was ended in this year’s final by Federer with the Croatian sobbing on court after suffering blisters.
The world number five put up much more resistance this time, winning the first set, and when Federer served at 4-4, 30-30 in the second it seemed Cilic might enjoy some redemption.
But the Swiss simply hates to lose and when Cilic netted a forehand he pounced to square the match.
A 100mph forehand service return gave Federer an early break in the decider and he turned on the style to race to victory.
Federer has reached the last four in 14 out of 15 appearances in the year-end tournament and will face David Goffin or Dominic Thiem for a place in the final. (Reporting by Martyn Herman, editing by Ed Osmond and Ken Ferris)