British number three James Ward suffered a straight-sets defeat by Russia's Mikhail Youzhny in the second round of the Dubai Championships.
Ward, ranked 177, was given a wild card into the event and beat Teymuraz Gabashvili on Monday to claim his first ATP victory outside the UK.
But sixth seed Youzhny proved too strong in round two, beating the 27-year-old Londoner 6-1 7-6 (7-3).
Youzhny will face Novak Djokovic in the quarter-finals.
Top seed Djokovic took just 57 minutes to beat Spain's Roberto Bautista-Agut 6-1 6-3 and is on course for a potential meeting with Roger Federer in the semi-finals.
The Swiss fourth seed Federer beat Radek Stepanek 6-2 6-7 (4-7) 6-3 and will face Czech Lukas Rosol in the last eight.
"Radek did a good job of putting the pressure on me and mixing it up," said Federer. "From that standpoint, it was a really difficult match. I'm very pleased to come through."
Third seed Tomas Berdych beat Sergiy Stakhovsky of Ukraine 6-2 6-1 to claim his eighth win in a row and set up a quarter-final against fifth seed Jo-Wilfried Tsonga.
German Philipp Kohlschreiber beat Andreas Seppi 6-3 6-3 and will play Tunisia's Malek Jaziri in the last eight.