The Red and Whites slipped to third after Nice's 2-1 home victory against Lorient the previous day, but first-half goals from Bernardo Silva and Fabio Coentrao gave them a deserved two-goal cushion at the break while Guido Carrillo and Helder Costa added further goals in the second half.
Toulouse had struck the woodwork in the fifth minute through right-back Somalia's thumping volley and squandered a chance to get back in the game when Wissam Ben Yedder's 38th-minute penalty was saved by Danijel Subasic after a controversial handball decision.
Monaco have now extended their unbeaten home league run to eight matches since a 3-2 defeat to Lorient in September, but remain 21 points adrift of PSG.
Reims edged one point clear of the relegation zone thanks to Algeria international Aissa Mandi's 89th-minute equaliser in a 1-1 home draw against St Etienne.
Jean-Christophe Bahebeck broke the deadlock for St Etienne when he slammed home Alex Soderlund's 60th-minute knockdown, but with the clock ticking down centre-half Mandi popped up at the far post to rescue a point for Reims, who have won only one of their last 14 league games.
Mid-table rivals Lyon and Marseille played out a 1-1 draw at the Parc Olympique Lyonnais where visiting goalkeeper Steve Mandanda produced a man-of-the-match performance.
Remy Cabella gave Marseille a 65th-minute lead before Lyon substitute Corentin Tolisso swept home a 79th-minute equaliser, but the point did little for either side's European aspirations.
Marseille striker Michy Batshuayi hit a post midway through the first half and had a 'goal' ruled out in the 74th minute for a dubious offside decision, while France goalkeeper Mandanda pulled off a string of fine saves to deny Lyon.
