Jordan Ayew scored a late winner to perhaps land the fatal blow to former club Marseille's title challenge and secure Lorient a vital win in their Ligue 1 survival battle.
The Ghanaian forward restored a lead which Lorient had twice surrendered late on before Mathias Autret made safe a 5-3 victory at the end of an exhilarating evening.
The result sees Lorient climb out of the relegation zone and up to 13th in the table and leaves Marseille eight points adrift of the summit with only four games remaining.
Ayew, who also scored in December's reverse fixture against the side that he left in the summer, scored one and supplied another to put the visitors two up inside 13 minutes at Stade Velodrome.
He skilfully volleyed a clever layoff from Romain Philippoteaux into the bottom corner with the outside of his right foot from 25 yards, and then headed a free kick back across goal for Francois Bellugou to nod home.
Older sibling Andre Ayew briefly threatened to steal his brother's thunder when he back-heeled Marseille to within one after Dimitri Payet's deep 58th-minute free kick had evaded everybody in the area and rebounded off the post.
The hosts were level on 67 minutes when Jeremy Morel powered Payet's wide delivery past Benjamin Lecomte, but their parity was short-lived as Philippoteaux soon drilled into the bottom corner from just inside the box.
Again though Marseille responded as substitute Michy Batshuayi beat the offside trap to divert Alaixys Romao's lofted pass beyond Lecomte on 76 minutes when no Lorient defender had bothered tracking his run.
However, Jordan Ayew was determined to have the last laugh and put Lorient in front for a third time when he dribbled through several defenders and lifted the ball into the roof of the net six minutes from time.
Autret beat Steve Mandanda at the second attempt two minutes later to condemn long-time league leaders Marseille to a fourth straight defeat and ensure that Ayew's heroics counted for the maximum.