A first half strike from South Korean forward Park Chu Young handed Ligue 1 leaders Lille suffered just their fourth loss of the season as Monaco moved out of the drop zone.
Lille have lost an important tie with a view to claiming their first league title in 53 years, as they could potentially see their lead cut to just one point should champions Marseille win at home to Toulouse tomorrow. Lille have 58 points from 30 games with Marsille four points behind.
The leaders were reduced to ten men after 37 minutes when Gervinho was given his marching orders, as their rivals showed a battling spirit which ensured they move out of the relegation zone into 14th place.
Monaco got off to an attacking start with Lille's defenders deflecting out an early effort from Cameroonian Benjamin Moukandjo after seven minutes. But it was a rough return from injury for Lille's Adil Rami as his back-pass to goalie Mickael Landreau allowed Park score the winning goal. Park made no mistake, picking up the pass to fire past Landreau in the Lille goal for his 11th goal of the season.
Although Lille monopolised the ball for long periods Rudi Garcia's side seemed tense and unable to create real chances.
Elsewhere, Paris Saint Germain got back to winning ways with a 2-1 success at Caen. The Parisians had been coming off a series of four matches without a win, but the victory means they stay fifth with 49 points with eight games to play.
Christophe Jallet opened for PSG after 13 minutes with Clement Chantome getting the second after 69 minutes. Romain Hamouma pulled one back for Caen three minutes into extra time.
European hopefuls Saint Etienne were held to a 2-2 draw by struggling Auxerre, while Bordeaux's European hopes took a knock as they were held to a goalless draw at home to tailenders Arles-Avignon.
Midtable Lorient and Sochaux drew 1-1 as did Valenciennes after a last-gasp goal by Marama Vahirua gave visiting Nancy a share of the points.
In the day's latest match, Rennes' faltering title challenge suffered another blow as they were defeated 2-0 by Brest at Stade Francis Le Ble. Goals from Nolan Roux and Bruno Grougi either side of half-time condemned Frederic Antonetti's side to a fourth match without victory.