Nearest rivals Aberdeen were held to a 1-1 draw at St Johnstone on Friday, but Celtic endured a frustrating goalless first half against the top flight's bottom side as they looked to capitalise.
Commons broke the deadlock via a deflected 52nd-minute strike before Ronny Deila's team closed out a victory that put them out in front with a game in hand.
Inverness Caledonian Thistle and Dundee United kept up their pursuit of the top two with respective wins over Hamilton Academical and Motherwell.
Third-placed Inverness condemned their opponents to a fourth consecutive league loss as player-manager Martin Canning endured a tough afternoon following official confirmation of his appointment at Hamilton.
Grant Gillespie put through his own goal in the 53rd minute and Nick Ross sealed a 2-0 win inside the final quarter of an hour.
Motherwell were beaten for a fifth time this month as fourth-place Dundee United triumphed 3-1 at Tannadice.
Charlie Telfer opened the scoring after the hour and Jaroslaw Fojut headed home to double United's advantage.
Simon Ramsden netted a volley to haul Motherwell back into the match but Telfer notched his second from the edge of the box in added time.
United's city rivals Dundee came from behind to beat second-bottom St Mirren 2-1, while Kilmarnock and Partick Thistle shared a 2-2 draw.
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