LONDON - Dominic Thiem keeps getting the better of Roger Federer.

Thiem beat Federer 7-5, 7-5 on Sunday in their opening match at the ATP Finals for his fifth win in seven meetings with the Swiss great - and third straight this year.

"To beat him, everything has to fit together. Today I think that was the case again," Thiem said. "Every time, only playing against him is a big honor. Beating him is even better."

Thiem broke in the opening game of the match and again for a 6-5 lead in the first set after Federer had leveled at 2-2.

The second set went with serve until Thiem broke at love for another 6-5 lead. Federer, a record sixtime champion at the ATP Finals, then missed two break points in the next game before netting a backhand return on Thiem's second match point.

Thiem also beat Federer at the Madrid Masters and in the Indian Wells final this year, but lost to him in the group stage at last year's ATP Finals.

For Federer, the loss means there's no room for another slip-up in his next two round-robin matches, against Novak Djokovic and Matteo Berrettini. He'll probably have to win both in order to reach the semifinals.

"It's a normal tournament from here on forward," Federer said. "Not allowed to lose anymore for me. That's how it is every week of the year for the last 20 years, so from that standpoint there is nothing new there."

Djokovic had a much easier start to the tournament, easing past Berrettini 6-2, 6-1 in their first round-robin match.

But despite a near flawless performance, Djokovic still found a way to berate himself.

Leading 4-0 in the second set against the Italian, Djokovic hit a backhand wide to concede a break and then turned toward his player's box and shouted out his frustration.

It was a clear sign that even at the end of another grueling season, Djokovic won't tolerate any dips in his game as he pursues a record-equaling sixth ATP Finals title.

"There's no other reasonable explanation (to that reaction) than trying to play as perfect as possible," Djokovic said. "But I guess that's me, you know."

It was certainly the same Djokovic that the O2 Arena crowd in London has become used to seeing. However, the second-ranked 32-year-old Serbian only needed to hit a total of 10 winners in the match as Berrettini's 28 unforced errors handed him an easy victory to start round-robin play.

Associated Press