Angel Di Maria opened the scoring and Uruguay striker Cavani found the back of the net twice after the break before Blaise Matuidi added a stoppage-time goal to put PSG back into second place with 71 points from 31 games, three behind leaders Monaco who beat Angers 1-0 on Saturday.
Nice, who have played an extra game, are third on 70 points after Mario Balotelli's double gave them a 2-1 victory at Lille on Friday.
Di Maria collected Cavani's through ball in the 56th minute before beating Karl-Johan Johnsson with a delicate chip after PSG had struggled in a dull first half.
Four minutes later, Cavani was perfectly set up by Adrien Rabiot and doubled the advantage with a low shot from inside the box.
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Cavani was at it again in the 70th minute, beating Johnsson from close range after being set up perfectly by Di Maria for his 29th league goal this season.
Midfielder Matuidi rubbed salt in the visitors' wounds with a fourth goal two minutes into added time.
PSG were without centre backs Marquinhos and Thiago Silva, who were both injured, but were barely bothered by a toothless Guingamp side.
Guingamp are 10th in the table on 41 points.
(Reporting by Julien Pretot; Editing by Clare Fallon)
