Porto scored a pair of valuable away goals to earn a 2-2 tie at Manchester United, and Arsenal drew 1-1 at Villarreal in the first leg of the European Champions League quarterfinals on Tuesday night.
United trailed for the first time in its title defence when Jonny Evans' poor clearance led to Cristian Rodriguez's fourth-minute goal. Wayne Rooney took advantage of a bad back-pass from Bruno Alves to tie the score in the 15th.
Carlos Tevez put Manchester United ahead in the 85th, but Porto substitute Mariano Gonzalez beat goalkeeper Edwin van der Sar in the 89th.
At Villarreal's Estadio El Madrigal in Spain, Marcos Senna's swerving shot from 20 yards evaded diving Gunners goalkeeper Manuel Almunia in the 10th minute off a feed from Guiseppe Rossi.
But Emmanuel Adebayor tied when he beat goalkeeper Diego Lopez with a bicycle kick in the 66th, after chesting a long ball from Cesc Fabregas.
Porto and Arsenal host the second legs on April 15, and the winners meet in the semifinals on April 29 and May 5. On Wednesday, Liverpool hosts Chelsea and Barcelona is at home against Bayern Munich.