After scoring a disappointing own-goal in Celtic's 2-2 draw at Dundee United last weekend, Ambrose redeemed himself with an impressive performance in the Scottish champions famous 2-1 win over four-time European champions Barcelona.
Kenyan midfielder Victor Wanyanma headed 'The Bhoys' into the lead from a corner kick in the 21st minute as Celtic managed to hold onto their lead going into the break.
In spite of pressure from Barcelona which saw them hit the woodwork on two occasions, it was Celtic that scored again to extend their lead after teenage substitute Tony Watt raced away to score in the 83rd minute.
Lionel Messi however got a consolatory goal for Barcelona in injury time, after latching onto the ball which was parried into his path from Pedro's initial shot.
Celtic now have seven points from four games, and are now just two points behind Barcelona in Group G.