Icardi netted his first at his second attempt after Steve Mandanda pushed out his initial effort in the 10th minute, and he headed beyond the advancing goalkeeper 16 minutes later to double the hosts' advantage.
Mbappe then turned in from close range in the 32nd after Angel Di Maria squared to him to make it 3-0. Mandanda got a hand to Mbappe's shot from the edge of the box a minute from halftime, but it was not enough to push it around his left-hand post as the France striker made it 4-0.
Andre Villas-Boas' Marseille is seventh after one win in six league games. Also Sunday, Rennes beat Toulouse 3-2 — ending a run of 10 matches without a win in all competitions — and climbed to eighth. Toulouse remains a point above the bottom three.
Saint-Etienne and Amiens drew 2-2.
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