The Principality side never looked back after Sedan's Johann Charpenet put through his own net on 34 minutes.
Sebastien Squillaci doubled the advantage five minutes later as Sedan rarely threatened Monaco's supremacy.
Sedan had Pierre Njanka sent off on 81 minutes for two bookable offences and with five minutes remaining Dado Prso (pictured) wrapped up the win.
The victory puts Monaco above Marseille on goal difference while Sedan slip into the relegation zone.
Nice stay level on points with Monaco and Marseille after a 1-0 home success against Guingamp.
Noe Pamanot grabbed the decisive goal on 42 minutes while the visitors had Florent Malouda dismissed in the second half.
Auxerre remain firmly in the title hunt after goals either side of half-time from Djibril Cisse and Philippe Mexes handed them victory at home to Sochaux.
Defending champions Lyon fluffed the chance to go top after a scoreless encounter at home to Nantes, who had Eric Djemba-Djemba red carded after 42 minutes.
Paris Saint Germain are only three points off the pace following a slender success at Strasbourg, which was sealed by an own goal on the hour mark from Jean-Christophe Devaux.
Bastia came from behind to nick a point at Ajaccio, who stay outside the drop zone on goal difference.
Bruno Rodriguez put the hosts ahead on 39 minutes but Franck Silvestre snared a draw for Bastia on 76 minutes.
Lens are perched in mid-table after a 1-1 draw at Rennes. John Utaka gave the visitors the lead on 39 minutes but the home team were level before the break courtesy of Cyril Jeunechamp.
Le Havre moved out of the bottom three after a late strike from Jeremy Henin snatched a win at home to Troyes.
The hosts had Jean-Michel Lesage sent off on 67 minutes but Troyes were reduced to ten men with three minutes remaining when Carl Tourenne received his marching orders.
Click below for an individual match summary:
Ajaccio 1-1 Bastia
Auxerre 2-0 Sochaux
Le Havre 1-0 Troyes
Lyon 0-0 Nantes
Monaco 3-0 Sedan
Nice 1-0 Guingamp
Rennes 1-1 Lens
Strasbourg 0-1 Paris Saint Germain
