European champions Manchester United were held to a 2-2 draw by Porto at Old Trafford 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 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.
Arsenal hold Villarreal
Emmanuel Adebayor's superb overhead strike secured Arsenal a 1-1 draw away to Villarreal in their Champions League quarter-final, first leg on Tuesday.
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 effort 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. "I don't even know how I scored that, but the most important thing was that the ball went into the back of the net," Adebayor told ITV.
"It was quite difficult for us because they played some very good football. The second leg is going to be tough, but we will do everything to get through. We got a good result to take home and we are very happy."
A match which started at a hectic pace, full of slick passing from both sides, was blown open when Senna's thunderbolt left Almunia with no chance.
Visiting defender Gael Clichy had already blocked an attempt from a corner on the line by then, but Arsenal responded with Samir Nasri testing keeper Diego Lopez at his near post in the 18th minute.