Novak Djokovic reached the semi-finals of the Dubai Championships with a 6-3, 6-4 victory over Marin Cilic on Thursday, while second seed Andy Murray pulled out with a virus.
Briton Murray, who has been feeling unwell since last month's Australian Open, withdrew before his quarter-final against France's Richard Gasquet.
"My temperature's up, sore throat, sore head, my body's aching a little bit, so I need to take some time off," the Scot told reporters.
Top-seeded Djokovic survived an onslaught from big-serving Croatian Cilic to secure victory.
"I think the key today was movement and focus," Djokovic said. "I was really trying to move well in the point, be patient, and just wait for the chances that have been given to me throughout the whole match because I was returning well.
"I knew he was going to be very aggressive... so I needed to be aggressive... and then [be] patient at the same time, which I think I did well."
Djokovic did not concede a point in his first three service games and at one stage he won three consecutive love games to earn a 4-1 lead.
But Cilic piled on the pressure as the Serb struggled to hold serve, fighting off two break points as he served for the set.
The first three games of the second set lasted 22 minutes as both players earned and lost break points before Djokovic sneaked ahead 3-2 with a crosscourt winner.
Djokovic failed to convert a match point on the Cilic serve at 5-3 when he was outwitted in a long rally.
But one game later he clinched victory with a crosscourt backhand volley.
Third seed Gilles Simon ended fellow Frenchman Fabrice Santoro's run with a 7-6, 6-1 win, while fourth-seeded Spaniard David Ferrer defeated Russian Igor Andreev 7-5, 6-1.
Set to retire at the end of this season, the 36-year-old Santoro reflected on his fortunes at the Middle East event. He reached the final of the first Dubai Championships in 1993 and won a remarkable final seven years ago when he climbed out of his sick bed to defeat Morocco's Younes El Aynaoui.
"I think that's the main memory because I remember that year, I was playing very good tennis and I reached the final," Santoro told reporters.
"And then the next 24 hours before the final was a tragic situation because I was feeling so bad. I was really, really sick, as sick as I've ever been in my life.
"Just a half-hour before the match, I thought I wouldn't be able to go on the court but I went out there and two hours later I came out with the trophy."