FC Porto and Arsenal Tuesday forced draws away at Manchester United and Villarreal respectively, gaining advantages into the second legs of the Champions League quarterfinals next week.

Substitute Mariano scored a last-minute equalizer for Porto to earn a well-deserved 2-2 draw, which was never short of thrills at Old Trafford.

The European champions appeared to have stolen another dramatic victory when substitute Carlos Tevez turned home Wayne Rooney's flick-on with five minutes remaining to put hosts ahead 2-1, but Mariano then sent their hopes hanging by a thread.

United's Premier League rivals Arsenal are in a better position to progress as Emmanuel Adebayor's stunning overhead kick earned them a crucial 1-1 draw.

Villarreal had dominated the first half and went in front when Marcos Senna fired in a screamer from 30 yards.

Arsenal improved and Adebayor headed wide before conjuring up his piece of magic. The Togo striker chested down a Cesc Fabregas pass and acrobatically volleyed home to silence the home fans.

Sir Alex Ferguson's side were struggling to do without injured center back Rio Ferdinando who failed to recover from a groin injury and Porto took advantage of the hosts' defensive vulnerability for a quick opening goal.

Cristiano Ronaldo conceded possession wastefully before defender Jonny Evans sent a poor clearance straight to Cristian Rodriguez, who cut in and curled a precise finish beyond Van der Sar to leave a roaring Old Trafford stunned after only four minutes.

Porto kept pressure on goal but United were gifted an equalizerthanks to an unlikely stupid mistake by Bruno Alves on 15 minutes.

The defender tried to find keeper Helton with a back-pass, unaware of Rooney on the move. Rooney welcomed the favor by coollylifting the intercepted ball over Helton.

Despite the setback the visitors continued to threaten, being presented with a host of chances to regain the lead.

Rodriquez headed straight at Van der Sar when well placed and Lopez was inches away from connecting with Lucho's pass at the farpost with no United defender in the vicinity.

Ferguson's decision to bring on Tevez proved to be a clever choice when he profited from Rooney's pass to power a finish at the near post on 85 minutes.

However, there was still time for Mariano to provide a final twist which denied Red Devils a celebration and left them a tough job heading to Portugal.