Andy Murray, who caused a great upset by beating world number one Roger Federer on Monday, followed it by almost stumbling to defeat to a relative unknown a day later.
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.
Then it was night time and cool and still; now it was bright sunshine with bluster and uncertainty.
Murray also had to adapt from a match in which he had very little pressure, except that of the need to play well, to being expected to win.
Verdasco intensified this pressure by taking risks in attack, sometimes causing Murray to plunge about trying to contain and retrieve. Sometimes too Verdasco hit unexpected winners with heavy, hard-to-read, left-handed blows.
He also took advantage quickly of Murray's sudden dip in standard in the second set and also fought back well in the final set after going 2-4 down.
But Verdasco was too often inconsistent, expressing his frustration at this near the end by launching a ball fiercely out of the stadium, a misdemeanour for which he was given a code violation warning.
Afterwards Murray claimed that his knee injury was not too serious to be able to play his quarter-final 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 percent 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 the 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.