Novak Djokovic out-battled Alexander Zverev to qualify for the last four at the ATP Finals on Friday, staying on track to match Roger Federer's record of six titles at the end-of-season event.

The Serbian top seed, who was beaten comprehensively by Daniil Medvedev in his second round-robin match, was again below his best at London's O2 Arena but did enough to win 6-3, 7-6 (7/4).

The five-time winner finishes second in Group Tokyo 2020 behind Medvedev and will play third-seed Dominic Thiem in the semi-finals on Saturday.

Second-seed Rafael Nadal, seeking his first win at the elite eight-man event, will face Medvedev in the other semi-final after finishing second in Group London 2020.

Djokovic broke Germany's Zverev at the first time of asking in the empty stadium and raced into a 3-0 lead, threatening to run away with the match - a repeat of the 2018 final, which Zverev won in straight sets.

The 33-year-old looked focused after his uncharacteristic mauling by Medvedev, serving himself out of trouble when he found himself trailing 15-40 in the seventh game.

That proved to be the last chance for Zverev in the set and 17-time Grand Slam winner Djokovic hammered a backhand winner down the line to take it 6-3.

Djokovic handed Zverev a break point in the fourth game of the second set after double-faulting but the German could not capitalise.

The 23-year-old fifth seed saved two break points on his serve in the following game, letting out a roar as he kept his nose in front.

The set went to a tie-break. Zverev earned an early mini-break but Djokovic levelled and the pressure was back on the German, who faltered to hand the Serbian victory.

The top seed said he had managed to find the right shots at the right time, in contrast to his performance against Medvedev, saying it was "anybody's game for most of the match".

He said Thiem, who won his first Grand Slam at the US Open in September, would be a tough opponent.

"Obviously earlier in his career he played his best on clay but of course being one of the hardest workers on the tour, the most dedicated players, Dominic found his 'A' game on all other surfaces," added Djokovic.

"His first Slam came on hard courts earlier this year in New York. I played him last year here -- I lost 7-6 in the third set. It was really a thrilling match. Hopefully we can have another great match but this time with a different outcome."

Djokovic, who recently equalled Pete Sampras's record of six year-end world number one finishes, has the chance to end the coronavirus-truncated 2020 season on a high by joining the absent Federer on six titles.

Medvedev will take on eighth-seed Diego Schwartzman, in the evening match, which is a dead rubber.

The O2 Arena is hosting the event for the 12th and final season before the championships move to Turin.

Novak Djokovic (SRB x1) bt Alexander Zverev (GER x5) 6-3, 7-6 (7/4)

Doubles

Playing later

Source: News24