World number two Djokovic made 46 unforced errors in Rome
In-form Spaniard Fernando Verdasco dumped world number two Novak Djokovic out of the Rome Masters, winning their quarter-final 7-6 (7-4) 3-6 6-4.
It was a gruelling encounter which ended after three hours and 18 minutes when Verdasco fired down an ace to book his place in the last four.
"The match could have gone either way - it was decided by one or two points," said Serbia's Djokovic.
Four-time winner Rafael Nadal beat Stanislas Wawrinka 6-4 6-1.
The world number three from Spain made a slow start against Switzerland's Warwinka, who only dropped two points in his first four service games.
But Nadal soon found his rhythm, breaking the Swiss in the ninth game before closing out the set.
I've had real problems with allergies for the past two months and this has been really troubling
And the 23-year-old Spaniard clinched the second set with little trouble to book his place in the last four.
"The first set was level for a long time. He was holding serve much easier than me," stated Nadal, who is chasing his fifth triumph at Foro Italico in six years.
"All the games on my serve were harder than his. But at 5-4 I started to play really well with some good drop shots."
Nadal will play either compatriot Feliciano Lopez or Latvian Ernests Gulbis in the semi-finals.
Clay-court specialist Verdasco has reached the final of his last two events - he lost to Nadal at the Monte Carlo Masters before going on to win last week's Barcelona Open.
Djokovic has been hindered by health problems of late but said he will be fit and ready for the French Open, which starts on 24 May.
"I've had real problems with allergies for the past two months and this has been really troubling," added Djokovic.
"But everything else is in order and I'm happy with the way I played, so definitely the French Open is the place where I want to get a good result.
"I was very close to victory and I know that this match could have gone either way."
Verdasco will now face compatriot David Ferrer, who beat Frenchman Jo-Wilfried Tsonga 6-4 6-1.
Meanwhile, Roger Federer's Rome exploits came to an end when he exited the doubles, along with Swiss Davis Cup team-mate Yves Allegro, following a 6-4 6-4 loss to American pair John Isner and Sam Querrey.