French champions Lyon went down to only their third defeat of the Ligue 1 season on Sunday as Monaco claimed a win at the Stade Louis II.
Goals from Ernesto Javier Chevanton and Marco Di Vaio put the Principality club firmly in charge of the match.
Substitute John Carew scored a stoppage-time consolation for Lyon but it was not enough to save the team that last weekend became the first ever French team to win five consecutive titles.
Monaco made a bright start and Jaroslav Plasil's 18-yard strike forced a fine save from Gregory Coupet.
Lyon made their first real threat on the Monaco goal after 18 minutes when Fred crossed the ball to Florent Malouda who could only find the side netting.
Chevanton then missed the target after Lyon skipper Claudio Cacapa had made a hash of his clearance from a Plasil cross.
Next time the Uruguayan got a sight on goal he was unerring as Di Vaio's pass released Chevanton who outpaced marker Cris amid appeals for offside before slotting past Coupet.
Monaco coach Francesco Guidolin had boasted before the match that his job was safe for next season and his players seemed to be backing their boss.
Lyon could have equalised after 43 minutes but Sylvain Wiltord, faced with only goalkeeper Flavio Roma, failed to beat the Italian custodian who made a fine save.
Lyon made a bright start to the second period and Malouda's cross was headed back to him by Fred but the former's volley was blocked by a Monaco defender.
Monaco made it 2-0 after 58 minutes when Chevanton's corner was headed down by Sebastien Squillaci towards Di Vaio and the Italian beat Coupet.
Lyon did not give up and Wiltord's shot was blocked before the former Arsenal man fired wide with the rebound.
Carew headed wide and then Roma had to grab a Malouda header as the champions finished strongly.
Gerard Houllier's side got on the scoresheet in stoppage time with an ultimately futile goal as Tiago's lob set up Carew who slotted home.