Jack Sock joined Roger Federer in the semifinals of the ongoing ATP World Tour finals after he defeated Alexander Zverev 6-4, 1-6, 6-4.
The American took the first set, as Zverev struggled to find his rhythm. But the German fought back to take the second in blistering style.
The third and final set was closely contested as the first, but it was Sock who emerged victorious after the 20-year-old Zverev doubled faulted, before sending another shot wide.
Sock sealed the win and will now face Grigor Dimitrov in Saturday’s semifinals.
Sock finished the group stage with a record of two wins, and a loss, which came in the match against Federer.
“That was a roller coaster match,” Sock, who becomes the first American in the last four of the World Tour finals since 2007, said after the match.
In the other match, Roger Federer came from a set down to see off Marlin Cilic 6-7(5), 6-4, 6-1.
Federer had already booked a place in the semifinals, but any hopes that this would be a stroll in the park was quickly extinguished as Cilic took the first test via the tie break.
It was a rematch of the Wimbledon final earlier in the year, but the Swiss had defeated the Croatian in straight sets that time.
In the second set, Federer had a chance to break early, but failed to take it, for the fifth time in the match.
However, the 19-time grand slam winner did regain his mojo to take the second set, after winning his first break point in his sixth attempt before racing to a 3-0 lead in the third set.
It was becoming easy for the former world number, as he broke once again before making it three wins in three.
In reaching another semifinals at the ATP finals, Federer has now reached the last four in 14 of 15 appearances in the year-ending tournament.
The eight-time Wimbledon winner will now wait for the winner between David Goffin and Dominic Thiem for a place in the final, as he chases a record seventh title in the event.
“In the beginning I was slightly over aggressive in the first set on some crucial points rather than maybe being patient,” Federer said. “I was able to turn that around late in the second set. Then just had a much better feeling in the third set.”
