A creative and spirited 10 man Monaco shocked Chelsea 3-1 in their Champions League semi-final first leg match, making Claudio Ranieri's expensively assembled squad look tired and ordinary.
Spearheaded by the wizardry of captain Ludovic Giuly, the young French team reacted to Andreas Zikos's harsh 52nd minute sending off with a fine display of counter-attacking football that left the competition favourites reeling.
Croat Dado Prso in the first half and Fernando Morientes and Shabani Nonda late in the second put Monaco on course for their first Champions League final.
Former France captain Didier Deschamps's side, whose average age is just 23 and who stunned Real Madrid in the quarter-finals, started brightly and took a deserved lead after 17 minutes.
Winger Jerome Rothen curled a free kick into the goalmouth, Chelsea striker Hernan Crespo missed the clearance, and Prso reacted sharply to head beyond Marco Ambrosio.
It was only the second goal Chelsea had conceded in seven away games in Europe this season.
The home team's lead was short-lived, however. Following a neat move down Chelsea's right flank England midfielder Frank Lampard crossed the ball and a tumbling Eidur Gudjohnsen managed to scramble it to Crespo who made up for his defensive lapse by firing it into the net.
Giuly should have added to the home side's score when he danced past John Terry and Wayne Bridge in the 34th minute only for Ambrosio to scoop the ball to safety.
But in the second half Chelsea coach Ranieri, dubbed The Tinkerman for his constant squad changes, brought on Argentine Juan Sebastian Veron for Danish international Jesper Gronkjaer on the left of midfield, one of several changes that appeared to destabilise the London side, who badly missed left-winger Damien Duff, out sick. Veron himself is making a gradual return to competitive football after missing nearly the entire season through injury.
Monaco upped the tempo with an all-out assault at the start of the second half as Prso went agonisingly close with a shot that Ambrosio punched away before Frenchman Marcel Desailly cleared off the line.
Their evening looked to have turned sour in the 52nd minute, however, when Greek midfielder Zikos was sent off after French midfielder Claude Makelele reacted theatrically to the lightest of cuffs as the two players got up from a challenge.
Makelele earned a yellow card, which means he will miss the return leg at Stamford Bridge on May 5.
After the dismissal, Ranieri brought on Dutch forward Jimmy Floyd Hasselbaink, but Chelsea looked more and more disjointed. They failed to impose themselves on the game and with the atmosphere becoming increasingly ill-tempered, defender John Terry was cautioned for a foul on Giuly who constantly outran him.
Giuly's counter-attacks left Chelsea exposed despite their superiority in numbers and it was no surprise when Morientes ran on to a Giuly pass in the 76th minute and unleashed a fierce shot into the top lefthand corner of Ambrosio's net.
It was the Spanish striker's eighth Champions League goal this season, which he is spending on loan from Real Madrid.
Giuly's 82nd minute replacement Shabani Nonda took only a minute to make his mark as his first touch steered the ball through Ambrosio's weak block.
It was Chelsea's first away defeat in the Champions League this season and with their home form less encouraging, Ranieri may well have to tinker some more if he is to find the victory necessary to earn a final berth against either Porto or Deportivo Coruna, who meet on Wednesday.
