Nadal’s 7-6 (7/3), 6-3 win over Gulbis, a gifted but unpredictable Latvian ranked just outside the top 20, means that he is within one win of another episode of his great rivalry with Roger Federer.
But the holder of three of the four Grand Slam titles could not capitalise on a good start, lacked his usual overwhelming physicality, and often left the ball in short, attackable positions for a hard-hitting opponent.
Indeed after relinquishing a 3-1 lead in the first set there seemed to be doubts about whether Nadal, who has been on antibiotics, would last if it developed into a long tough tussle.
Nadal called for the doctor, apparently feeling unwell.
He was told to drink more and that if he didn’t feel better soon he might then think about whether or not he wanted to continue.
That caused Nadal to call out rather alarmingly “water, water, water”, but although his performance remained below par, he always seemed the likely winner after surviving the tie-breaker.
The highlight of his effort was a brilliant plunging volley from a fierce passing shot by Gulbis at 30-40 in the sixth game of the second set, just when a break of serve might have lifted his young opponent to a higher level.
After closing that game out for 4-2 he began to see the finish line and appeared to find extra energy as he did so.
“I just did the best I could today,” said Nadal. “I started well, and I pushed him to make many mistakes. I will be more ready for my next match.”
His semi-final opponent will be Nikolay Davydenko, the defending champion from Russia, who overcame the steep serving of Ivo Karlovic, the former top 20 Croatian, by 6-3, 7-5.
Davydenko beat Nadal in a sensational final last year, losing the first set to love and saving two match points in the process.
“I will be ready for him this time,” Nadal stressed.
Federer was not at his best either, but reached his eighth successive semi-final since losing his Wimbledon title six months ago by outplaying Viktor Troicki 6-2, 6-2.
Federer passed up fully seven break points before breaking through for 4-2 in the second set, but there were still some signs of the improved form he has enjoyed since his association with coach Paul Annacone.
There was also a surreal phase, late in the first set, when Federer’s acceleration into a 5-2 lead coincided with a burst of noisy and colourful fireworks, as if they had been planned as an accompaniment to his explosive arts.
“I thought it was a very concentrated performance,” said Federer. “I really thought I saw the ball a bit better.”
“I really had many, many chances throughout the match, and obviously eventually I was able to break through and make it difficult for him.”
“From my side, I’m really happy the way I was able to keep him on the back foot, make him feel like he didn’t know what was coming his way. That’s the kind of tennis I like to play, so it was really a good match for me.”
Federer now has a semi-final against Jo-Wilfried Tsonga, who is seeking his first title in 15 months after a long spell with knee problems, and who progressed with a 7-6 (7/4), 7-6 (11/9) win over Guillermo Garcia-Lopez, the seventh-seeded Spaniard.
“It’s nice to see him back,” Federer said of the charismatic Frenchman. “Injury is not a fun thing to go through, and he’s had a fair share of them.
“It’s exciting playing him again. I think he’s a very explosive player with good character, and good for the game.”