The singles matches at the ATP World Tour Finals have so far been significantly one-sided, with all eight round-robin contests through the first four days being settled in straight sets.

Six of the of the first 16 sets were decided by a 6-1 score, and Wawrinka dropped a 6-0 second set to Novak Djokovic in their meeting. According to calculations by, the first eight matches went a total of eight hours and 26 minutes.

Thursday's encounter between Kei Nishikori and David Ferrer went three sets, but ended 6-1 in the third. Ferrer was substituting for an injured Milos Raonic and could not qualify for the semifinal stage.

"No, I don't have any explanation," said Wawrinka, who has contributed to the lack of competitiveness in two ways: He delivered a 6-1, 6-1 defeat of Tomas Berdych in his first match, and then went down 6-3, 6-0 to Djokovic.

The men's field had looked more open than previous years, given the Grand Slam breakthroughs by Wawrinka and Marin Cilic, as well as Kei Nishikori reaching the final of the U.S. Open. However, Djokovic and Roger Federer have dominated the tournament through the first few days.

"I think it's a big surprise for everybody," said Wawrinka. "For us also. It's so strange because this year everybody before the tournament was expecting some big matches because was more surprise during all the year with me winning Grand Slam, Cilic also; Raonic, Nishikori being there. So everybody was expecting some big match."

And rightly so, he added. "The expectation, yeah, are right because that's the top eight, actually nine, players of the year who are playing the best tennis. If you look all the past years, it was always some good match, some tough one, three-setter match."

Djokovic also said he had no explanation, but expected some tighter contests in London.

"I don't. You know, obviously I can't speak in the name of the other players, so I don't know how they feel on the court," he said. "I know that I've been playing very well this week and hope that I can continue this way. Now, of course, since it's the tournament of the best eight players in the world, people, fans, the crowd expect to see a little bit more excitement and longer matches. So far we didn't have any three-setters. I think that's going to change as the tournament progresses."

However, Federer suggested a slow court was a reason, saying, "I think it's actually quite simple, in my opinion, because the court plays somewhat slow, and the serve doesn't have that much of an impact depending on you how back it up, your serve.

"You need to hit a lot of great shots, if it's not working well for you, to have an impact. You have to work extremely hard. I think if you then look at the way Novak or Stan has played here, I think they both played very well, which made it very difficult for the other guys.

"From that standpoint, I think the best movers are most likely going to come through here."