Lorient condemned Guingamp to their third Ligue 1 defeat and secured local bragging rights with a second-half blitz as they won 4-0 at the Stade du Moustoir.
Sylvain Ripoll's side turned the screw after a goalless first half, with Benjamin Jeannot tapping them in front after 58 minutes.
Substitute Valentin Lavigne (twice) and Jordan Ayew then added gloss to the scoreline with a flurry of three goals in the last 10 minutes.
Defeat leaves Las Costarmoricains in 17th place, while Lorient climb to sixth - two points off the summit.
The visitors gave as good as they got early on, with midfielder Claudio Beauvue forcing a good save from Benjamin Lecomte in the first few minutes.
The 26-year-old had another chance five minutes before the interval but he could not find the target with his header at the far post after Thibault Giresse did well to get a cross in from the left.
Moments later Lorient gave notice of their forthcoming dominance as Gilles Sunu forced Mamadou Samassa into a desperate save and then Rafidine Abdullah struck the crossbar from the edge of the area a minute later.
Nifty footwork on the left from Lamine Kone crafted the opener as Lionel Mathis was turned inside and out before Kone rolled it to Jeannot, who made no mistake from close range to notch his first Ligue 1 goal.
Sunu was heavily involved in Lorient's second as the hosts found more joy down the left flank, with Lavigne latching on to Sunu's ball into the box to beat Samassa with 10 minutes to go.
Things then got worse for Guingamp as Lavigne pounced pounced on a soft clearance from Christophe Kerbrat to put Ayew in for a cool finish from close range.
Lorient rounded off the victory with another surging counter-attack down the left, with Raphael Guerreiro this time making progress before finding Lavigne in acres of space at the far post to ram home in the final minute.