Andy Murray, who caused a great upset by beating world number one Roger Federer, followed it on Wednesday by almost stumbling to defeat to a relative unknown.
The 20-year-old Briton had to survive a jittery final set tie-break before getting through 6-3, 3-6, 7-6 (7/5) against Fernando Verdasco, the world number 30 from Spain.
Murray finished looking relieved and emotionally drained, as well as appearing to suffer discomfort in his right knee.
His mobility was reduced from early in the second set, and thereafter he relinquished most of his ambition to attack, relying upon containment and a liberal sprinkling of errors from Verdasco.
"You are relieved when you come through a match you have not played well," Murray admitted. "And it's difficult to explain; especially when you have been 6-2 up in the tie-break and it gets to 6-5."
At that dramatic moment the two men played by far the longest rally of the match - more than 30 shots - with Murray eventually luring Verdasco into over-hitting.
"I wasn't feeling comfortable. I was swinging at the ball so hard and it was landing halfway up the service box," Murray said with a humourless laugh.
This happened partly because of a strong breeze which made accuracy difficult to achieve and which created conditions totally unlike those in which Murray had played Federer.
Afterwards Murray claimed that his knee injury was not too serious to be able to play his quarterfinal against Nikolay Davydenko with as good a chance as usual of winning.
"I have been doing a lot of stuff for it," he said. "I don't know if the muscles are a little bit tired but I get it a lot just after a couple of games.
"I get it in 50 per cent of my matches. It's just a bit uncomfortable for a few games. If it was really bad I would have had the trainer on."
He was also asked if this match was the kind of grind which Federer had warned Murray risked by playing too passively behind the baseline and relying on running.
"The problem today was that I was missing it too early in the rallies, shanking a lot of balls, missing returns and not feeling comfortable at all," Murray said.
"The match didn't feel too much of a grind, but it was a difficult match, I didn't play well and I am glad to get through."
Murray now has a chance to capitalise against an opponent, Davydenko, whom he has beaten on the last three occasions.
The fifth-seeded Russian came through with a 6-1, 6-4 victory over Jan Hernych of the Czech Republic.
Two seeds were beaten.
Richard Gasquet, the seventh-seeded Frenchman, lost 6-3, 6-4 to Igor Andreev, the Russian who trains much of the time on Spanish clay courts and who finds the high-bouncing Dubai hard courts to his liking.
Andreev made a great start, taking the first three games after Gasquet double faulted to drop serve, and consolidating the advantage throughout the first set.
Both men then held serve four times in the second, until Andreev snatched the match-winning break in the penultimate game, again with the help of a Gasquet double fault, this time for 30-all.
Earlier eighth-seeded Czech Tomas Berdych was dismissed 6-2, 7-5 by Spanish left-hander Feliciano Lopez.
Berdych came back from 2-5 to 5-5 in the second set as he strove to avoid a one-sided defeat but found Lopez, who delivered ten aces, in good form and keen for a quarterfinal with his compatriot David Ferrer, the world number four.
Another notable name to make an exit, possibly for the last time, was Fabrice Santoro, the 35-year-old who won an amazing final in 2002 but now was beaten 6-3, 7-6 (7/3) by Australian Open champion Novak Djokovic.
However Santoro weaved enough of his old magic with spins and tactical variations to lead 3-1 in the second set, prompting Djokovic to admit: "I was starting to lose my hair in the second set."
It avenged his loss to Santoro in the Masters Series in Paris in November.
"It was an honour to have played against such a very special player," Djokovic said.
The world number three now plays Andreev, while Rafael Nadal, the French Open champion, takes on Andy Roddick, the former US Open champion in the last quarterfinal.