Alexander Zverev set a last four match against Roger Federer in the ATP finale after losing John Isner 7-6 (7/5), 6-3 on Friday while Novak Djokovic will take on Kevin Anderson. Zverev played American giant John Isner at London's O2 Arena and knows that a win of any kind would take him to the semifinal in the season-long tournament. The turning point in the round robin match came at the end of the 12th game when the 21-year-old German saved a focal point on his own earning an ace, continuing to force a tie.
The players changed minipauser, but the giant Isner again fell on his own to hand over the seat to Zverev – meaning he no longer had a chance to qualify for the last four.
In the second set, a single break in service in the eighth game proved crucial when Zverev served the match.
"I'm incredibly pleased to be in the semi-finals," he told Sky Sports.
"John is such a tough opponent. The last two matches against him (Marin) Cilic and I could have gone in any way. The first set was incredibly tight. I'm just happy to be on. I will prepare myself for tomorrow's best. "
Djokovic will play Cilic later on Friday but it's now a dead rubber because Cilic can not mathematically reach the semifinals.
Third seed Zverev has won three titles this year, including the Madrid champions, but although he is often referred to as next-generation leader, his record in Grand Slams is bad and he will be desperate to make a statement in London.
Zverev is the youngest semifinalist at ATP Finals since Juan Martin del Potro 2009.
Second-seed Federer, chasing his 100th title, shot Anderson in straight sets to the top of the Lleyton Hewitt Group on Thursday, but both players evolved, which means early exits for Kei Nishikori and Dominic Thiem.
Djokovic enters his evening match against the Australian Open finalist Cilic with the luxury of already knowing that he has qualified the top of the Guga Kuerten group.
Serbian world number one has had a remarkable renaissance during the second half of the season after elbow surgery and indifferent shape earlier in the season.
He has lost only two matches since the beginning of July and won Wimbledon and the US Open under the road and grew up again as the man hit when he tried to pull out with Federer on six ATP Finals titles.