World number two Roger Federer is through to the last four at the ongoing season-ending ATP Finals in London after he saw off tournament debutant Alexander Zverev in three sets.
Federer, 36, defeated his German opponent 7-6 (8-6) 5-7 6-1 at the O2 Arena to move into last four.
Third seed Zverev can still qualify for the semis if he can beat American Jack Sock in his final group match on Thursday.
The eighth seeded Sock had earlier beaten Croat fifth seed Marin Cilic 5-7 6-2 7-6 (7-4) to stay in contention for a slot in the next stage.
Speaking afterwards, the American was very excited with his win. He said: “That was a tough one for sure.”
“It’s been an interesting morning so far, the fire alarm went off at 4am and we had to exit the building. But I love playing here in London, it’s an amazing atmosphere, you make me feel like [I’m] home.
“I’m just excited to win and keep myself alive.” he concluded.
In the Pete Sampras Group on Wednesday, Grigor Dimitrov will face David Goffin before Dominic Thiem of Austria play against Pablo Carreno Busta, a replacement for the injured Rafael Nadal.