LONDON: Even the best player in the world can have an off day, especially when he’s playing someone many believe is the best of all time.

Roger Federer brought his top game to the O2 Arena on Tuesday, stopping Novak Djokovic’s ATP Finals winning streak at 15 by beating the top-seeded Serb 7-5, 6-2.

The world number one would probably have beaten most players, even with the errors piling up and his serve out of sync, but not Swiss great Federer who sealed a semi-final spot at the season-ending tournament for the 13th time in 14 appearances with a match to spare.

“I wouldn’t have picked it maybe before the tournament, just because of his really good record on the indoors, the year he’s had,” said Federer, who lost to Djokovic in the Wimbledon and US Open finals.

Three-time defending champion Djokovic, on a 23-match winning streak, suffered his first defeat since losing to Federer in the Cincinnati final on August 23.

Djokovic’s first indoor loss since 2012, means he needs to beat Czech Tomas Berdych on Thursday to be sure of joining Federer in the semi-finals.

Japan’s Kei Nishikori beat Berdych 7-5, 3-6, 6-3 in the day’s early offering, the first three-set match so far.

While it earned Nishikori another $167,000, the reward for a group win, it is likely to prove in vain unless he beats Federer in his final match and Berdych defeats Djokovic.

Djokovic could even scramble through with a three-set defeat, providing Nishikori does not win.

“These kind of things happen. I have to accept it and hopefully work on it tomorrow and get better in the next one,” Djokovic told reporters.

Djokovic had been untroubled until the 12th game when Federer earned a couple of set points, converting the second with a sublime half-volley dink off a dipping Djokovic backhand.

A tired-looking Djokovic backhand slice into the net gave Federer a 2-0 lead in the second set, and although the Swiss six-times champion gifted back the break, he raced away to a 5-2 lead and claimed victory on his second match point.

Earlier, eighth-ranked Nishikori survived a second set wobble but recovered to beat world number six Berdych thanks to what he admitted was a “lucky” shot.

Both players lost their Finals group stage opener — Nishikori to Djokovic and Berdych to Federer. A second defeat for Berdych therefore left his semi-final hopes hanging by a thread.

In the third and deciding set, Nishikori saved a break point at 3-3, the key moment in a match that lasted two hours and 23 minutes.

“Last shot, I went for it, closed my eyes. [It] was a little bit lucky I made that shot,” he said.

Published in Dawn, November 19th, 2015