Postiga, who is Portugal's leading goalscorer in World Cup qualifying, was then sent off for a tame headbutt on McAuley.
Alves's opener arrived on 20 minutes and it was a fine guided volley from the edge of the area, which came after Oliver Norwood's header had failed to properly clear Joao Moutinho's outswinging set piece.
The Fenerbahce full-back has now scored four times during the current qualifying campaign.
Cristiano Ronaldo, who was shown a yellow card for his protestations at Postiga's dismissal has been kept fairly quiet so far.
The Real Madrid star has registered just one shot at goal.