Roger Federer dropped a Grand Slam set for the first time since the 2006 US Open but still powered into the French Open semi-finals with a 7-5, 1-6, 6-1, 6-2 win over Spain's Tommy Robredo.
The top seed overcame the rare second set lapse to romp to his eighth consecutive win over the Spanish ninth seed.
Federer will now take on either Russian fourth seed Nikolay Davydenko for a place in the final.
The victory also kept him on course for a widely-anticipated title showdown on Sunday against double defending champion Rafael Nadal who plays his quarter-final against fellow Spaniard, and 1998 winner, Carlos Moya tomorrow.
'It's never easy to play Tommy especially on clay, it's his favourite surface,' said Federer.
'Sadly I had too many errors in the second set but overall it was a good test.'
Federer, bidding to make history at Roland Garros by becoming only the third man to hold all four Grand Slam titles at the same time, broke Robredo in the opening game of the first set before the 25-year-old levelled at 2-2.
Robredo handed the break back in the 11th game and the Swiss world number one took the opener when Robredo went long with a lob.
But the Spaniard, who had won only one set in his career against Federer coming into this quarter-final, battled gamely in the second set and broke in the second and sixth games to take it 6-1.
It was the first set Federer had lost at a Grand Slam since the final of the US Open last year, an 11-match-in-a-row record he shared with John McEnroe.
However, the ten-time Grand Slam title winner made Robredo pay for his insolence by racing through the third set with breaks in the second and fourth games to take it 6-1 in just 20 minutes.
He finished it with an ace just to hammer home his displeasure.
Federer took a 3-0 lead in the fourth set, having won nine games in ten, with Robredo desperately trying to stay in touch with a break back to trail 1-3.
The top seed, however, shattered any hope of a Robredo revival by breaking again to lead 5-2 before he turned on a mini-cameo of three sumptuous volleys to take the match.
Davydenko overcame Argentine baseliner Guillermo Canas 7-5 6-4 6-4 to set up the semi-final showdown with Federer.
World number four Davydenko, 26, showed more composure when it mattered to reach the last four at Roland Garros for the second time in three years.
The 29-year-old Canas, who returned to action last September after a 15-month doping ban, was bidding to make the semi-finals of a grand slam tournament for the first time.
He has now fallen in the quarter-finals in Paris three times.
Davydenko looked in control throughout a tight contest and converted the first match point with a superb forehand winner after just three hours of play.
RESULTS:
4-Nikolay Davydenko (Russia) beat 19-Guillermo Canas (Argentina) 7-5 6-4 6-4
1-Roger Federer (Switzerland) beat 9-Tommy Robredo (Spain) 7-5 1-6 6-1 6-2
