LONDON (AP) ― His body already aching after a season of almost unceasing success, Novak Djokovic ran into a brick wall in David Ferrer.

Ferrer’s relentless hitting proved too much for Djokovic on Wednesday, giving the fifth-seeded Spaniard a 6-3, 6-1 win and a spot in the semifinals of the ATP World Tour Finals.

“I think today maybe was my best match of the season,” Ferrer said.

The exact opposite was true for Djokovic. The winner of three Grand Slams and 10 titles overall this season looked far from the player who dominated most of 2011, and lost for only the fifth time this year.

“I just wasn’t there,” said Djokovic, who has won 70 matches this year. “It was the worst match I’ve played this season so far definitely.”

Starting when he was ahead 3-2 in the first set, the slumping Serb lost seven straight games. He made 33 unforced errors, exactly three times as many as Ferrer.

Djokovic can still advance to the semifinals if he beats fellow Serb Janko Tipsarevic on Friday, but he isn’t hopeful.

“If I don’t play at least 50 percent better than I did tonight, I don’t think I’ll have any chance,” he said. “You always hope that tomorrow will bring something better. That’s the way I’m thinking now.”

Tipsarevic, who stepped in for injured Scotsman Andy Murray, has no chance of reaching the last four after he was beaten in three sets by Tomas Berdych in Wednesday’s earlier match.

Berdych saved a match point en route to a 2-6, 6-3, 7-6 (6) win to maintain his hopes of progressing from Group A.

Djokovic was dressed all in black for the evening match save for the flashes of gold on his shoes, while Ferrer wore a more traditional white outfit, but it was the Spaniard’s tennis that dazzled the crowd at the O2 Arena.

Ferrer’s energetic retrieving around the baseline appeared to sap the belief from Djokovic, who spent much of the second set shooting pained looks at his support camp or shrugging his shoulders in despair.

When Djokovic blazed a forehand wide and long to give Ferrer the match in 1 hour and 15 minutes, it was the Spaniard’s turn to shrug his shoulders, as if in disbelief.

“It was a surprise, no?” said Ferrer, who also beat Murray in straight sets in his opening match and joined Roger Federer in qualifying for the semifinals with a match to spare.

Ferrer’s win followed another surprisingly one-sided match between Federer and Rafael Nadal on Tuesday evening. Federer won 6-3, 6-0 and both Djokovic and Nadal lost 10 of the last 11 games in listless performances.

Nadal said he thought on Monday that he might have to withdraw from the tournament with a shoulder problem. Murray did pull out on Tuesday with a groin injury.

With Federer the only one of the top 4 players without any health issues, the debate about the length of the season is set to continue.

“It’s a subject that needs to be discussed in the future,” Djokovic said. “I think the people in the ATP are willing to help. It’s going to be a long process.”

Berdych had lost his opening match against Djokovic despite holding a match point, but he turned the tables in Wednesday’s afternoon match when Tipsarevic put a difficult volley just wide when leading 6-5 in the deciding tiebreaker.

“I was a bit unlucky on Monday. I got luckier here,” Berdych said. “So, you know, 1-all.”

Tipsarevic double-faulted for only the second time to give Berdych his first match point, and the Serb slipped on the baseline to allow Berdych to put away a forehand winner.

Tipsarevic said his knee was hurting after his fall, but he didn’t expect second alternate Nicolas Almagro to be called into action for Friday’s match against Djokovic.

“We’ll see what’s going to happen when I cool off,” Tipsarevic said. “But my feeling now is that I will be ready for practice tomorrow afternoon.”