Porto's Lucho Gonzales (L) scores the opener past Besiktas Ali Tandogan (right) during their Group A Champions League match at the Dragao stadium on Tuesday.
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Goals by Gonzalez and Ricardo Quaresma gave Porto a 2-0 victory over Besiktas and a place in the Champions League last 16.
Gonzalez gave the Portuguese side a controversial 44th minute lead after Besiktas keeper Rustu Recber and his defenders stopped momentarily, expecting an offside decision, leaving the Argentine midfielder to steer the ball into an empty net.
Porto, who were Champions League winners in 2004 and needed only a draw to go through, made sure of a place in the knockout phase when fellow midfielder Quaresma burst clean through to rifle home their second goal in the 62nd minute.