Dan Carter looked to have earned Racing 92 victory in Lille, but Frederic Michalak got Toulon over the line with the final kick of the game.
A last-gasp penalty from Frederic Michalak secured a 21-20 victory for Toulon over Racing 92 in a thrilling meeting between two Top 14 title contenders at Lille's Stade Pierre Mauroy.
Racing looked set to take over from Clermont Auvergne at the top of the table, for 24 hours at least, when Dan Carter converted his own 76th-minute try to secure a two-point lead.
However, Martin Castrogiovanni was then penalised in the last minute and veteran fly-half Michalak split the posts with the last kick of the game, sending Toulon above their opponents and up to second.
Toulon can also claim to have landed a significant psychological blow ahead of their European Champions Cup quarter-final against Racing, which takes place on April 10.
Prior to the late drama, Toulon had led by 12 points, but Wenceslas Lauret crossed with seven minutes remaining and Carter's score appeared likely to prove decisive, only for Michalak to ultimately settle matters.
Another title challenger, Montpellier, also moved above Racing courtesy of a 45-21 victory at bottom side Agen. Bismarck du Plessis and Timoci Nagusa shared four of the visitors' six tries.
Like Toulon, Brive left it late to claim victory –Gaetan Germain converting an injury-time touchdown from Arnaud Mignardi as Castres were beaten 23-22.
Jonathan Wisniewski contributed two tries, four conversions and two penalties as Grenoble overcame a sluggish opening half-hour to beat La Rochelle 39-23, while Pau beat Oyonnax 25-6.
Leaders Clermont face Bordeaux-Begles on Sunday prior to Toulouse hosting struggling Stade Francais.