Frenchman Fabrice Santoro thrilled the home crowd by crushing world number three Novak Djokovic 6-3, 6-2 in the second round of the Paris Masters on Wednesday.
Djokovic, a revelation this season with five titles and a final appearance at the US Open, was a shadow of his brilliant best.
Roger Federer was again stretched by Croat Ivo Karlovic, before the Swiss prevailed 6-3, 4-6, 6-3.
World number two Rafael Nadal, making his debut at the $2.45 million (1.2 million pounds) indoor event, had no such problems. The Spaniard recovered from a break down to outclass Italian Filippo Volandri 6-3, 6-1 and set up a third-round match against Swiss Stanislas Wawrinka.
Russia's Nikolay Davydenko, who won the tournament last year and is seeded fourth, overcame a sluggish start to move past Argentine qualifier Juan Martin Del Potro 7-6, 6-1.
Djokovic, who entered the Bercy hall wearing a Zorro mask which he took off when the match started, made a string of unforced errors.
"It's been a very long season and I'm really exhausted," said the 20-year-old Serb. "I hope people will understand. You can't be at 100 percent all the time."
Santoro, who has a reputation for upsetting big names and had knocked out world number five Andy Roddick last week in Lyon, double-faulted on his first match point but made amends with a backhand volley on the second to seal victory after 69 minutes.
The resilient 34-year-old next faces Andy Murray, who had earlier stayed on course for a Masters Cup berth by beating Finn Jarkko Nieminen 7-6, 6-3.
The 20-year-old Scot, who won his third career title on Sunday in Russia, is one of several players fighting for the two remaining spots at the November 11-18 season-finale in Shanghai featuring the world's top eight.
Murray took the first-set tiebreak 7-5 when Nieminen hit a backhand into the net.
Nieminen broke serve in the fourth game of the second set but Murray hit back immediately before capturing the Finn's serve again in the seventh game.
Murray, who escaped unhurt from a car accident in Paris on Monday, stayed in control until Nieminen bowed out with an unforced error on the second match point.
"Santoro is my favourite player to watch," Murray said. "You won't see a game style like his probably for the rest of my career. He's just a completely different player, plays some unbelievable shots."
Results:
6-James Blake (U.S.) beat Nicolas Mahut (France) 6-7(3), 7-6(4), 6-1
1-Roger Federer (Switzerland) beat Ivo Karlovic (Croatia) 6-3. 4-6, 6-3
David Nalbandian (Argentina) beat 14-Carlos Moya (Spain) 6-4, 6-4
10-Richard Gasquet (France) beat Jo-Wilfried Tsonga (France) 7-5, 7-6(3)
Marcos Baghdatis (Cyprus) beat 13-Ivan Ljubicic (Croatia) 6-4, 7-6(4)
2-Rafael Nadal (Spain) beat Filippo Volandri (Italy) 6-3, 6-1
4-Nikolay Davydenko (Russia) beat Juan Martin Del Potro (Argentina) 7-6(3), 6-1
Fabrice Santoro (France) beat 3-Novak Djokovic (Serbia) 6-3, 6-2
Stanislas Wawrinka (Switzerland) beat 16-Juan Ignacio Chela (Argentina) 6-3, 6-1
15-Andy Murray (Britain) beat Jarkko Nieminen (Finland) 7-6(5), 6-3