Defending champion Novak Djokovic made it through to the quarter-finals.
But seeds Andy Murray and Jo Wilfried Tsonga were both casualties in the second round of the Barclays Dubai Tennis Championships.
Nikolay Davydenko also had to bow out when he was forced to retire from his match against Michael Berrer with a wrist injury.
Defending champion Djokovic was made to work by Viktor Troicki to reach the last eight in temperatures of 34C at the Aviation Club before Murray was dumped out by Janko Tipsarevic and Tsonga fell in straight sets to Ivan Ljubicic.
Djokovic prevailed against his Serbian compatriot Troicki, the world number two eventually claiming a 3-6 6-4 6-2 victory in two hours and six minutes.
World number four Murray, playing his first tournament since losing in the Australian Open final to Roger Federer, lost in three sets to Serbia’s Tipsarevic.
The 22-year-old Scot looked to have overcome losing the first set when he took the second to force a decider, but Tipsarevic raised his game to seal a 7-6 (7/3) 4-6 6-4 victory in two and a half hours.
Tsonga, the fifth seed, had no answer to Ljubicic who produced 15 aces in a 7-5 6-3 win which set up a meeting with Djokovic.
Sixth seed Marin Cilic saved three set points from a 3-6 deficit in the second set tie-break to beat Austrian qualifier Stefan Koubek 6-2 7-6 (8/6) and he will now face Austrian Jurgen Melzer, who claimed a 6-3 7-5 win over Tommy Robredo.
Seventh seed Mikhail Youzhny beat Bjorn Phau 7-6 (7/2) 6-4 and will face Tipsarevic.
World number 56 Berrer advanced to his third ATP World Tour quarter-final this season when Russian Davydenko retired because of an injury to his left wrist after losing the first set 6-3.
Marcos Baghdatis beat Indian qualifier Somdev Devvarman 6-3 3-6 6-1 and will now take on Berrer.