The result left United in fifth place, a point behind Arsenal who have a game in hand, and two adrift of Manchester City, as the battle for Champions League spots appears set to go down to the wire.
"I was very happy for Matteo, two times he was involved in the goals," Van Gaal told Manchester United television (MUTV).
"I was very happy with the performance and I think it was a four or five to zero game. We should have finished it much earlier and scored much more goals."
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Playing in an adventurous formation with Wayne Rooney deployed in a deeper role behind the front four, United were denied a bigger win by a string of superb saves from visiting goalkeeper Julian Speroni.
The 36-year-old Argentine kept out a barrage of stinging shots from Anthony Martial, Juan Mata and Jesse Lingard after Delaney's own goal.
He was powerless to stop Darmian's thunderbolt, however, after the Italian chested down a poor clearance by Palace on the edge of the area and let fly, with the ball cannoning in off the post.
The result put Van Gaal in a positive mood for Saturday's FA Cup semi-final against Everton at Wembley.
"I came to England to win titles and now we are very close, but first we have to beat Everton and that is not easy," he said.
(Writing by Zoran Milosavljevic; Editing by Toby Davis)
