United had won all four Group F games heading into Tuesday night's clash - and it looked like Carlos Tevez's 61st-minute equaliser had earned them a point after Fernando Abel had given the visitors a shock lead on 22 minutes.

But Ronaldo, playing against his former club, drilled home a 20-yard piledriver in stoppage time to ensure the Red Devils take top spot in Group F.

Ronaldo set up the first chance of the game for Louis Saha, who dragged his shot wide from eight yards.

Joao Moutinho flashed an effort across the face of United's goal, which was breached on 22 when Abel caught keeper Tomasz Kuszczak napping at his near post with a swerving right-footed drive from wide on the right flank.

It should have been 2-0 on 26 minutes but Liedson's goal was wrongly ruled out for offside - and Anderson Polga's volley stung Kuszczak's hands before the interval.

Sir Alex Ferguson sent Tevez and Ryan Giggs on from the bench for the second half - and the Argentinian equalised when he bundled in Ronaldo's scuffed shot towards goal.

That put some fire in the Red Devils' bellies, and after Miguel Veloso's 20-yard shot hit the roof of the net, visiting keeper Rui Patricio had to sharp to deny Ronaldo and Owen Hargreaves with his legs.

But he could only watch in admiration as Ronaldo's thunderous free-kick sailed past him in the dying minutes of the game.