European champions Manchester United were held to a 2-2 draw by Porto at Old Trafford last night to leave their Champions League quarter-final on a knife-edge ahead of the second leg in Portugal next week.

Both teams scored in the dying minutes with Carlos Tevez putting United 2-1 up after 85 minutes and Mariano equalising for Porto in the 89th.

The enterprising visitors took the lead after four minutes when Cristian Rodriguez fired a low left-foot shot past Edwin van der Sar after a poor clearance from Jonny Evans.

United scored a fortuitous equaliser after 15 minutes when Bruno Alves lost concentration and sent a woeful backpass straight to Wayne Rooney who waited for goalkeeper Helton to commit himself before firing into an empty net.

United extended their record unbeaten Champions League run to 22 matches but failed to gain the advantage they wanted from an open and entertaining match.

In the other quarter-final first leg of the night, Emmanuel Adebayor's superb overhead strike secured Arsenal a 1-1 draw away to Villarreal.

The game was only 10 minutes old when Villarreal midfielder Marcos Senna received the ball outside the area and scored with a fierce drive that flew into the top corner.

Arsenal were hindered by first-half injuries to goalkeeper Manuel Almunia and defender William Gallas who both had to be substituted, as Villarreal dominated.

But the Londoners responded in the second half and Adebayor's acrobatic strike from Cesc Fabregas's pass in the 66th minute left the visitors with an away-goal advantage for the return leg in London on April 15.