Goals from Wayne Rooney, Juan Mata and Robin van Persie secured an ultimately comfortable triumph for Louis van Gaal's team but it would have been a different story without De Gea's heroics at the other end.
Three fine stops from Raheem Sterling extended the England forward's scoreless run for club and country to 21 matches and De Gea displayed razor-sharp reactions to twice deny half-time substitute Mario Balotelli.
A sixth straight league triumph leaves United third in the table, five points behind neighbours Manchester City and a further three shy of leaders Chelsea.
"We have to go step by step, game by game," De Gea told Sky Sports
"We want to be in first position but we need to keep training hard and playing like this.
"I'm really happy with the three points against Liverpool, of course.
“We played a very good game, we scored three goals and that's fantastic.
"In the first half I saved two against Sterling and the second half Balotelli. We scored three goals and it is unbelievable."
Van Persie led the plaudits for De Gea and also paid tribute to United's defensive unit, where midfielder Michael Carrick was a reassuring presence in the middle of a back three.
"I think overall we played a good game and David was outstanding again," he added.
"He was absolutely brilliant, like he always is
"In those games it is always important to score first. It gives you an extra bit of calmness and I think, although at times we were a bit sloppy, overall we kept the ball well.
"Carrick made a big difference at the back. He is so comfy on the ball.
"[Phil] Jones, Jonny [Evans] - all the back four, five played really well, They were very calm."
