Roger Federer of Switzerland in action against Evgeny Donskoy of Russia during their men's singles second round match of Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates on March 1, 2017. [Photo/VCG]

Federer, who saw his eight-match win streak in 2017 ended, did not want to make excuses and said it had nothing to do with a leg injury picked up at the Australian Open, where he beat old foe Rafael Nadal in the final in his last appearance before Dubai.

"I just think it's still the beginning of the comeback and I've got to take the positives out of playing again a tournament where I feel I'm quite healthy. I'm just happy I got over the injury I sustained at the Australian Open," he said.

Federer led 5-1 in the third-set tiebreaker, but Donskoy refused to fold.

"I had my chances," Federer said. "I should have somehow closed it out. I don't know how it got away, but he did very well, and, yeah, it's a rough one for sure."

Federer, who skipped last year's tournament because of arthroscopic knee surgery, was in the hunt for an eighth Dubai title.

The initial excitement in the match occurred with Federer leading 6-3, 3-4 when one set of the court floodlights went dark. Fans in the crowd turned on their cellphone flashlights and started waving them in the air.

Both players then agreed to play on, despite the problem and two games later full lighting was restored.

"I felt, if he wants to keep playing, I'm happy to keep playing," Federer said. "I didn't want to wait. It wasn't quite dark yet."

Donskoy will play seventh-seeded Lucas Pouille in the quarterfinals. Pouille defeated qualifier Marius Copil 6-1, 6-4.