Rennes came out on top in an extraordinary Ligue 1 match which was delayed by 10 minutes after their fourth goal sparked a pitch invasion.
Julien Feret struck from an indirect free-kick in the penalty area after goalkeeper Guillermo Ochoa handled Carl Medjani's back-pass but a section of Ajaccio supporters, angered by the taking of the free-kick, stormed from the stand to protest.
Referee Ruddy Buquet suspended the game until order was restored and Rennes held on for victory.
They had twice come from behind in the first half, Feret and Romain Alessandrini equalising after goals from Adrian Mutu and Fousseni Diawara. Cheick Diarra put them ahead for the first time before Feret's controversial clincher.
The match started at a high tempo, with Ochoa saving from Alessandrini before Mutu put the hosts ahead with a little over a minute on the clock.
Benjamin Andre crossed for the Romanian to control and fire past Benoit Costil, having got ahead of defender Onyekachi Apam.
Feret levelled from the penalty spot in the 16th minute, sending Ochoa the wrong way after Diawara fouled Alessandrini.
Ochoa denied Jonathan Pitroipa but there was otherwise little of note until the 41st minute, when Medjani headed Johan Cavalli's corner goalwards and Diawara, virtually on the goal line, nodded home.
But Rennes quickly responded when Alessandrini hammered a free-kick from the edge of the box past Ochoa to make it 2-2 at the interval.
Mutu went close from a free-kick just after the restart but Rennes edged ahead just before the hour mark. The influential Alessandrini crossed and Diarra headed home from close range.
But the match descended into controversy in the 72nd minute when Medjani flicked the ball up with his foot before heading it back to Ochoa, who picked it up.
With Medjani's actions covered by FIFA Law 12 as an attempt to circumvent the back-pass rule, Buquet correctly awarded a free-kick, which was taken by Alessandrini. The ball did not appear to roll its full circumference before Feret lashed it home, sparking the anger of the Corsican fans - though the amended version of Law 13 states simply ``the ball is in play when it is kicked and moves''.
Buquet took the teams off the pitch while the unrest was quelled, and after a 10-minute delay a pedestrian final quarter-hour was played out, with Costil's save from Cavalli the only incident of note.
The result lifts Rennes to fourth place ahead of the winter break, while Ajaccio are just three points above Sochaux, who occupy the third spot in the relegation zone and play Toulouse tomorrow.