Jeremy Pied's early goal claimed a shock 1-0 win for Guingamp over defending Ligue 1 champions Paris Saint-Germain on Sunday.
Pied headed in the only goal of the game in the 10th minute before Guingamp battened down the hatches and held on to their lead, with Jonas Lossl making a key late save to deny PSG talisman Zlatan Ibrahimovic.
The win is a much-needed boost for strugglers Guingamp who moved up to 13th place with the victory, while PSG remained one point behind leaders Marseille, who could extend the gap if they take any points from Monaco at Stade Louis II in the late kickoff.
The victory was the second this week for Guingamp, who qualified for the Europa League round-of-32 on Thursday, while it is the second successive defeat for PSG after they lost 3-1 at Barcelona in the Champions League.
The game got off to the perfect start for the hosts when Thibault Giresse delivered a free kick from outside of the area into the box, where Pied headed in from close range.
Lossl then made a decent save to deny Marco Verratti with a strike from 20 yards before Claudio Beauvue sent a close range shot narrowly wide at the other end from Younousse Sankhare's ball in.
PSG keeper Salvatore Sirigu blocked another Giresse free-kick 10 minutes before the break as Guingamp finished the half in the lead and on a high.
After the interval, PSG came out with more purpose and Ibrahimovic almost levelled in the 46th minute with a shot from the far post, which Lossl blocked with difficulty.
Guingamp had a good counter-attack a couple of minutes later when Sankhare released Beauvue on the left, the midfielder beating David Luiz before racing towards goal, with Sirigu deflecting his shot behind.
PSG were not yet beaten, though, and with just a shade over 10 minutes left on the clock, Verratti freed Lucas, who made a few yards more with the ball then tried his luck from 20 yards, which went inches over the bar with Lossl beaten.
Guingamp were left sweating in the 86th minute when PSG sparked an attack which almost resulted in Ibrahimovic levelling the score.
Blaise Matuidi freed Gregory van der Wiel who picked out the Sweden international at the far post for a low volley, which Lossl denied with another fantastic save.
Guingamp then saw out the remaining minutes to claim the valuable win.