Alexander Zverev boosted his ATP Finals hopes with victory over Diego Schwartzman in London.

Zverev will now face world number one Novak Djokovic on Friday with a semi-final spot still a possibility.

Djokovic plays Daniil Medvedev in the second Group Tokyo 1970 match from 20:00 GMT at the O2 Arena.

Zverev, who won the tournament in 2018, lost his opening match to Medvedev on Monday.

Neither Schwartzman or Zverev were at their best in a flat match, with Zverev ultimately finding enough consistency to edge his way to victory.

"It was better than Monday and I'm excited for Friday. That's probably the most difficult match-up I could have, playing Novak," Zverev said.

"I said from the beginning of the week in every match I'm going to improve. I needed to get back into the rhythm.

"I went in with the mindset that I had to win and I will do that again on Friday."

Schwartzman claimed an early break in the opening set but Zverev fought back, winning four games in a row to take a 4-2 lead.

The Argentine cut a frustrated figure, his forehand in particular letting him down, and it looked as though Zverev was on his way to a routine win when he took the first set.

The US Open finalist started the second set well, breaking Schwartzman for a 3-1 lead, before his opponent finally fought back.

Schwartzman came through an eight-minute service game and Zverev responded with a terrible service game of his own, sending down four unforced errors that allowed Schwartzman to break.

After Schwartzman took the second set, Zverev seemed to dial back into the match. Again, he broke early and this time made it count, his first serve and strikes down the line once again finding the mark.

Zverev will, however, need a much improved performance if he is to beat Djokovic in their final round-robin match on Friday.