The French goalkeeper was desperately unfortunate on 21 minutes, as Rodrigo's powerful long-range effort rebounded off the crossbar, hit him on the back and bobbled into the net.
Carrasso was at the heart of the action again early in the second half.
This time, he made a superb point-blank save to keep out Oscar Cardozo's bullet header.
Benfica were good value for their victory and the Portuguese outfit were rarely troubled in defence.
Abdou Traore's late volley, which whistled narrowly over the crossbar, was as close as the visitors came to scoring an away goal.