Coming on as a second-half substitute, Pereira regularly beat his man using a variety of tricks and body feints and he generally looked lively.
He was also unlucky not to score after his fizzing shot went just wide of the post.
Pereira has bags of potential and his display may persuade van Gaal to start him against San Jose Earthquakes on Tuesday night.
Elsewhere, Morgan Schneiderlin may get the nod ahead of Bastian Schweinsteiger in the middle of the park after his similarly impressive performance against Club America.
Van Gaal appears keen to bed Schweinsteiger in rather than throwing him in at the deep end. In any case, it is good to see that United finally have some midfield options ahead of the new campaign.