Celtic suffered a shock 1-0 defeat at home to Inverness CT on Saturday, while Aberdeen moved into third in the Scottish Premier League.
A second half strike from Billy McKay was enough to separate the two sides and hand the defending champions their third defeat of the league campaign.
McKay’s 64th-minute goal was the sixth the Celtic defence have conceded at home in the league this season, having gone the whole of last season with only conceding six at Parkhead.
Neil Lennon’s side, who were beaten in the UEFA Champions League midweek, started the brighter of the two, with both Commons and Victor Wanyama unleashing efforts.
Inverness’ best chance of the half came when Owain Tudur-Jones played in Andrew Shinnie, but unfortunately for the Scotland international, his shot went well wide of Fraser Forster’s goal.
Celtic continued on the front foot at the start of the second half, but they could not find a way past the Inverness defence, as Commons was forced to try his luck from long range.
Inverness took a shock lead after some superb play by Philip Roberts on the right hand side of the box saw the midfielder beat two Celtic defenders before playing the ball across to McKay, who had the simple task of knocking the ball home.
Terry Butcher’s Inverness continued to defend for their lives during the closing stages of the game and they managed to survive, meaning they move up to fifth – three points adrift of Celtic.
A 77th-minute goal from Niall McGinn helped Aberdeen to a hard-fought 1-0 at Hibernian.
McGinn pounced on a failed clearance as he calmly guided the ball into the net at Easter Road.
Saturday’s result moves Aberdeen on level points alongside Hibernian with a game in hand.
In other matches, Rowan Vine netted a match-winning goal in the dying moments as St Johnstone edged 10-man Kilmarnock 2-1, while Steven Thompson bagged a brace in St Mirren’s 3-1 triumph at home over Dundee.
Dundee United toppled Ross County 2-1 and Hearts held Motherwell to a scoreless draw.