DOHA, Qatar (AP) — Gael Monfils upset Rafael Nadal 6-3, 6-4 Friday in the semifinals of the Qatar Open to line up an unexpected all-French final against Jo-Wilfried Tsonga after Roger Federer pulled out of the tournament with back spasms.

Monfils, who had only beaten Nadal once before in nine meetings, used a strong first serve and chased down nearly every shot.

“I just played my game,” said Monfils, who defeated Viktor Troicki of Serbia to reach the semifinals. “I think last night I played a good match and felt very good about it. I knew today if I did it in same spirit against Rafa, it would be great.”

Monfils broke Nadal to go up 4-2 in the first set. Nadal recovered to lead 4-1 in the second set but Monfils stepped up his game. He won 16 of 21 points — including several jump volleys — to go 5-4 up before closing out the match when Nadal hit a return wide.

Monfils said the key was not getting rattled, even when down in the second set.

“It was just a break, so I was just trying to adjust the way I played,” he said. “I was just thinking, ‘it’s one break and I know I can break him.’”

Nadal praised Monfils for his performance, saying he had “fantastic shots with very good backhands, good forehands, his movements were fantastic.”

The match was overshadowed by Federer withdrawing only 30 minutes before his match against Tsonga. The 16-time Grand Slam winner said his back had not improved since beating Andreas Seppi in three sets on Thursday.

Federer, who was looking for his fourth title in Doha, apologized to organizers but said he didn’t want to risk further injury ahead of the Australian Open, which starts Jan. 16.

It is only the second time the 30-year-old Swiss has pulled out of a tournament due to injury in his illustrious career. He withdrew from the quarterfinals at the 2008 Paris Masters, also because of a back injury.

“I don’t feel a whole lot of improvement for today, and I just don’t think it’s the right time to risk anything more right now,” said Federer, who has tried several treatments. “I still have pain and that’s why it was the only right decision, a difficult one for me ... so it’s a sad moment for me and for the tournament and for the fans, but health goes first.

Federer said he felt the injury Wednesday in the first set against qualifier Grega Zemlja.

“Then I wasn’t able to serve properly anymore,” Federer said. “Had the same thing yesterday. I was really playing, you know, with the hand brake on, and I was just trying to manage the situation, really. So it wasn’t very easy to deal with.”

Federer plans to fly out of Doha on Saturday as scheduled and is hopeful he will recover by the end of the week with rest and more treatment.

“For Australia, I’m optimistic, just because it’s not very good but it isn’t crazy bad,” Federer said. “I have had bad backs in the past. This is definitely not very good, otherwise I would be playing. But I feel without play and the right treatment, I will get through it in the next few days.”

Nadal dismissed suggestions that the loss was a setback to his preparations for the Australian Open.

“I go to Australia very happy about what I did here. For sure I would love to win the tournament, win today, have another match tomorrow,” Nadal said. “The only negative thing of today is to lose. For the rest of the things, I am satisfied.”

Tsonga has won two out of three matches against Monfils.

“It’s really always tough to play against Jo because he have a powerful game and kind of game, you know, it’s tough to manipulate him from the baseline,” he said. “So I need just to focus also on my game and focus on my mind.”