The City midfielder produced a captain’s display for his country in Algeria’s opening Group C clash in Cairo, Egypt, leading from the front and causing Kenya constant problems.
And Mahrez set the seal on a fine individual display by doubling the North African side's lead just before half time after an earlier 34th minute penalty by Baghdad Bounedjah had given them the lead.
Mahrez struck on 43 minutes, guiding home a left-footed shot from the centre of the box.
The result left Algeria level at the top of Group C on three points with Senegal, who beat Tanzania 2-0 earlier on Sunday.
Algeria’s next match is against the Senegalese on Thursday, kick-off 6pm BST.