LONDON     -     Defending champion Alexander Zverev reached the last four at the ATP Finals with a 6-4 7-6(4) defeat of Russian debutant Daniil Medvedev on Friday and consigned Rafael Nadal to an early exit at the same time.

The 22-year-old German served superbly throughout and held his nerve in the second-set tiebreak to notch a second group victory and claim second spot ahead of world number one Nadal.

Spaniard Nadal had earlier beaten group winner Stefanos Tsitsipas 6-7(4) 6-4 7-5 in a near three-hour battle to keep his hopes alive but needed Medvedev to do him a favour by beating Zverev.

Medvedev, 23, dropped his opening service game and never made much of an impression on his opponent’s 140mph serve.

He double-faulted at 3-4 in the tiebreak to give Zverev a two-point lead and Zverev finished it off with an ace.

While it was a great night for Zverev, it was disappointing for those who had hoped to see a Nadal versus Roger Federer semi-final on Saturday.

With five-time champion Novak Djokovic also knocked out, 26-year-old Dominic Thiem will take on 22-year-old Zverev for a place in the final.

“The young guys have been playing much better tennis than they were maybe last year,” Zverev, who beat Federer and Djokovic back-to-back to win the 2018 title, said.

“I think the biggest surprise is actually that Novak is out of the tournament, because ... this court, the conditions is the best fit for his game.

The other thing is obviously Rafa. Nobody expected him to be out from our group. Our group, for me and Stefanos to qualify, I don’t think a lot of people would have picked that.”

Zverev has not played Thiem this year but trails 2-5 in head-to-heads. “I hope it will be a back-to-back for me, but I have a very difficult semi-final tomorrow,” he said. “He’s been playing some unbelievable tennis, maybe the best tennis that we have ever seen from him.”