Donaldson's brace ensured the Bees took three deserved points and claimed the psychological advantage ahead of the sides' Johnstone's Paint Trophy clash on Tuesday
A defensive blunder from Bees right-back Shaleum Logan handed Crawley a route back into a game, his wayward back pass dropping for former Bee Nicky Adams to bundle home from close range.
Rosler said: "It was very important to get the three points after the midweek draw, and I thought we deserved it with some excellent performances.
"I told Clayton he needed to step up this season and told him to make the runs into the box and not wide. He did that and got his rewards."
He added: "Crawley are a similar side to us in many ways. Physical, strong, creative with players who can change a game. Because of that I'm delighted that we have come out on top by playing the kind of good, possession and passing football we were at the start of the season."