Top-ranked Novak Djokovic has survived a second-set challenge to dismiss Argentine eighth seed Leonardo Mayer 6-3 7-5 to reach the Qatar Open semi-finals.
Mayer made four unforced errors on Thursday when serving for the second set at 5-4 which opened the door for Djokovic to secure a straight-sets victory.
He will play Czech Tomas Berdych in the last four against whom he has a 21-2 winning record. Berdych beat Kyle Edmund of Britain 6-3 6-2.
"I think I've played better first and second sets, but credit to him for being solid and going for his shots," Djokovic said. "The second set was very close and it could've gone his way. It was a good test to see where I am."
Despite being broken four times, second-seeded Rafael Nadal advanced to the semis with a 6-3 5-7 6-4 win over Andrey Kuznetsov of Russia.
"He played so crazy with amazing shots," said Nadal. "It's true that I missed the serve more times than what I wanted. I think I played a great third set because, if not, I will not be in that semi-final."
Nadal will face Illya Marchenko. The Ukrainian, who beat fourth-seeded David Ferrer in the first round, defeated seventh seed Jeremy Chardy of France 6-3 7-6 (7-3).
"I saw him play during the whole week," said Nadal. "He's playing fantastic. The match against David was great, and today against Jeremy he played amazing, too. He's playing with big confidence."
