For the first time in this year's tournament, the eight-time champion dropped a set.
And this had to be on Nadal's mind: His opponent, David Ferrer, could present real problems. Not only is Ferrer ranked No. 5, and not only was he the runner-up at Roland Garros a year ago -- to Nadal, of course -- but he also beat Nadal on red clay the last time they played each other.
So how did Nadal handle this test? Perfectly. From late in the second set, he won 10 games in a row, and 13 of 14 the rest of the way, to come back and beat Ferrer 4-6, 6-4, 6-0, 6-1, setting up a semifinal Friday against Wimbledon champion Andy Murray.
''At the beginning,'' Nadal acknowledged, ''David was playing with a higher intensity than me.''
But once Nadal made a key adjustment, deciding to dispense with backhands and hit forehands as much as possible, he took over. After committing 28 unforced errors across the first two sets, Nadal had zero in the third, and only three in the last.
Ferrer, for his part, said that in the latter stages, ''I lost my concentration, my focus.''
It was Nadal's 33rd consecutive win at the French Open and improved his record in the event to 64-1.
The route Murray took during his 6-4, 6-1, 4-6, 1-6, 6-0 victory over No. 23 Gael Monfils of France was far more circuitous, finishing right on the cusp of dusk after 9:30 p.m. In front of a crowd loudly pulling for Monfils at Court Philippe Chatrier, Murray was terrific at the outset, mediocre in the middle, then closed on a high.
After a brief discussion with a tournament official over whether there was enough sun to play the fifth set -- there are no artificial lights on the Roland Garros courts -- Murray made the whole thing moot. He raced through that set in 24 minutes, winning 24 of 31 points, as Monfils appeared to stop trying.
Earlier, No. 4 Simona Halep of Romania and No. 28 Andrea Petkovic of Germany both moved into the semifinals of a Grand Slam tournament for the first time. They'll face off Thursday for a spot in the final. Thursday's other semifinal will be 2012 champion Maria Sharapova against 18th-seeded Eugenie Bouchard of Canada; they won quarterfinals Tuesday.
In Wednesday's women's matches, which preceded the men's quarterfinals on the two main courts and began after a three-hour rain delay, Halep beat 2009 champion Svetlana Kuznetsova 6-2, 6-2, and Petkovic defeated 2012 runner-up Sara Errani by that very same score.
Kuznetsova took a medical timeout after the opening set because her left hamstring was bothering her, and she returned with a bandage on that leg.
''Maybe it wasn't her best day today,'' Halep said, ''but for me it was the best.''
A year ago, Halep arrived at Roland Garros ranked 57th. But over the past 13 months, she's won seven titles -- more than any woman other than Serena Williams -- and been better and better at Grand Slam tournaments. She got to the fourth round at September's U.S. Open and the quarterfinals at January's Australian Open.
Petkovic, meanwhile, is enjoying a resurgence. She made it to the top 10 in 2011, when she was the only woman to reach three major quarterfinals (although she went 0-3). In late 2012, she hurt her right knee, and her ranking plummeted to 177th last year. But she's worked her way back, and after eliminating Errani, the gregarious Petkovic kissed her racket - something she said she'd never done before.
''I don't know what happened to me. I was just overwhelmed by emotion,'' Petkovic said. ''I had no boy to kiss, so I kissed my racket, right?''