Jack Sock overcame an Alexander Zverev fightback to knock out the young German player with a 6-4, 1-6, 6-4 win that books him a semifinal with Grigor Dimitrov. Earlier in the day, Roger Federer kept his perfect record.
Alexander Zverev's hopes of ending his breakthrough year with a bang were extinguished by American eighth seed Jack Sock in a match that Sock described as a "rollercoaster" in London on Thursday night.
The German, 20, was up against it early on, as Sock demonstrated the baseline skills that got him past Marin Cilic earlier in the tournament to take the first set 6-4.
But suddenly everything changed as Zverev rattled through the second set conceding only a single game as all his powerfully-struck shots came off, leaving Sock with no answers.
The momentum seemed to stay with the young German as he broke his opponent in the first game of the decider but then things started to go badly wrong. Zverev double-faulted in his service game before unforced errors handed the initiative back to Sock, who gratefully accepted to break again when Zverev hit another double fault in his next service game.
The match took another twist as Zverev broke back in game seven but his vulnerability on serve reared its head again in the tenth as Sock punished more errors.
"That was a rollercoaster match. I didn't have the hottest start in the third but I kept in there and kept fighting," Sock said. He'll play Grigor Dimitrov in the last four.
Federer does it again
In the group's earlier match, Roger Federer eased past Cilic to make it three wins from three for the Swiss and end Cilic's tournament.
The 36-year-old, who had already qualified for the semifinals, recovered from an early setback to take the re-run of this year's Wimbledon final 6-7 (5-7), 6-4, 6-1 and book himself a day off before Saturday's semifinals.
Federer finished with 17 aces and saved the sole break point he faced,to make it 52 wins and four losses in an incredible comeback campaign.
"I'm just happy I'm playing a great season," he said afterwards. "I'm so happy that I was able to reach this level of play and still being able to play also at the end of the year."
"It wasn't just, like, one tournament at the beginning, then nothing after that. So it was just throughout I've had a great year.
"I have no regrets (about missing out on number one to Rafael Nadal) because I totally over-exceeded my expectations. Just happy I'm injury-free and healthy right now, enjoying myself still."
Federer will play Dominic Thiem or David Goffin in the other semifinal.
mp (DPA, Reuters)