Zverev sets up Federer last-four clash at ATP Finals

Alexander Zverev set up a last-four clash against Roger Federer in the ATP Finals after seeing off 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 knowing a win by any scoreline would take him through to the semi-finals of the season-ending 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 set point on his own serve with an ace, going on to force a tie-break.

The players swapped mini breaks but the giant Isner then faltered again on his own serve to hand the set to Zverev -- meaning he no longer had any chance to qualify for the last four.

In the second set a single break of serve in the eighth game proved decisive as Zverev served out the match.

"I am unbelievably happy to be through to the semi-finals," he told Sky Sports.

"John is such a tough opponent. The last two matches for him against (Marin) Cilic and me could have gone either way. The first set was unbelievably tight. I am just happy to be through. I will prepare myself the best for tomorrow."