Novak Djokovic's status as the man to beat at the ATP World Tour Finals was enhanced by a demolition of Stan Wawrinka last night.

It was the eighth successive match at the O2 Arena to be decided in straight sets but there was no shortage of quality on show from Djokovic.

The world number one has now won 29 matches in a row indoors and it would be hard to bet against him making it 32 to take the title after his 6-3 6-0 victory.

Djokovic is still not quite through to the semi-finals, with Group A in exactly the same complicated position as Group B.

The two-time defending champion will need a set against Tomas Berdych tomorrow to be sure, while Marin Cilic is not out of the reckoning despite a 6-3 6-1 thumping by Berdych earlier yesterday.

Wawrinka ended a run of 14 straight defeats against Djokovic in the quarter-finals of the Australian Open in January before going on to take the title.

And it looked like the Serbian could be in for a tough time when Wawrinka came out firing with his groundstrokes and opened up a 2-0 lead.

But in the next five games he won only three points, paying for too many errors against the ultra-consistent Djokovic.

Wawrinka had to try to force the issue, though, with Djokovic close to his metronomic best.

The Swiss dug in to save a set point and at least halt the run of games against him, but it was a temporary reprieve as Djokovic reeled off seven games in a row, clinching victory with a pinpoint forehand winner.

The top seed can clinch the year-end world number one ranking with victory over Berdych, who put his poor start to the tournament behind him with a much-improved display against US Open champion Cilic.

The pair both lost their opening matches 6-1 6-1 in the joint heaviest defeats since the tournament moved to Britain in 2009.

This was revenge for Berdych, who lost to Cilic both at Wimbledon and during the Croatian's stunning run in New York.

The Czech maintained his odd record of having lost his first match and won his second on each of his five appearances in London, which has only once been good enough to take him through to the semi-finals.

Berdych will probably have to beat Djokovic to reach the last four, a feat he has managed just twice in 18 meetings.

Their last match in the final of the China Open last month was the most chastening of the lot, with Berdych losing 6-0 6-2 after Djokovic served for the match at 6-0 5-0.

"I'm going to try to maybe get three, four games," he said with a smile. "That would be better from the last time.

"That experience was really an experience. As I said after my first match, it couldn't be worse than that. So let's see. It's pretty much the same scenario."

It was not the way Cilic wanted his debut appearance to pan out, and he said: "Of course, it's a little bit disappointing to play like this. I was not expecting it. But I feel a little bit tired, and my body feels a little bit tired on the court.

"It seems that the things I'm doing are all basically going in a wrong direction."