(CNN) -- Roger Federer refused to blame an ongoing back problem after being dumped out at Indian Wells by long-term rival Rafael Nadal.
Federer, who could now drop to World No.3 should Andy Murray reach the final, was beaten 6-4 6-2 by the Spaniard.
The 31-year-old looked to be playing through the pain barrier during his last-16 win over compatriot Stanislas Wawrinka just 24 hours earlier.
But the 17-time grand slam winner did not use his back complaint as an excuse for his performance as his quest for a record fifth triumph at Indian Wells fell flat.
"[It was the] same as against Stan. I mean, I could play," Federer told reporters.
"I'm happy to be out there and able to compete. But it's obviously a small issue."
Instead, Nadal avenged last year's semifinal defeat by the Swiss and took his record to 19-10 in matches against Federer.
But the manner of victory was not lost on Nadal, who was quick to acknowledge the limitations of his opponent.
"I played a fantastic first set, in my opinion. The second set was strange," said Nadal.
"The second set, I think Roger didn't fight as usual. He probably had some problems and he didn't feel comfortable enough to keep fighting.
"Both of us tried to play our best. I played much better than yesterday.
"My movements today were much, much better than yesterday, so I'm very happy for that, especially after a long match yesterday, to be able to compete well the next day."
This was the earliest the pair had met in a regular tournament since 2004, when Nadal won their first meeting in the third round of the Sony Open Tennis in Miami.
The 26-year-old will now face Tomas Berdych in his eighth consecutive semifinal at Indian Wells.
The women's quarterfinals were blighted by injury after defending champion Victoria Azarenka and seventh seed Sam Stosur both pulled out with injury.
Azarenka, ranked two in the world, was forced to withdraw with tendinitis and inflammation in her right foot and ankle.
"That's frustrating for me as a player, not knowing," Azarenka told reporters after revealing she is unsure of her recovery time.
"Sometimes you think, OK, well, I rest three days and I'm going to be fine with it. But when you don't know the healing process it's a little bit frustrating."
Stosur's calf injury gifted Germany's fourth seed Angelique Kerber a place in the last four where she will now play Caroline Wozniacki.
In the other semifinal, 2006 winner Maria Sharapova will face fellow Russian Maria Kirilenko.
It is the first time Kirlenko has made the final four at Indian Wells following wins over Agnieszka Radwanska and former Wimbledon champion Petra Kvitova.