Benzema has now scored in six consecutive matches in all competitions for the first time since 2016.
Benzema curled a shot into the bottom corner to give Madrid the lead in the 20th minute after being released by a fine piece of play from Toni Kroos, who danced past a defender before taking out three more with a pass into the feet of his teammate.
Kroos was again involved for the second goal arriving on the half-hour mark, winning the ball back on the edge of the box and allowing Benzema to dribble across the box and score his eighth goal in six matches in all competitions.
Santi Mina headed Celta back into the game before the break following a free kick and the hosts improved in the second half while the visitors ran out of steam.
Madrid wrapped up the points for Madrid with a stoppage-time counter attack when Benzema crowned his exceptional display by sending in a cross to Asensio, who walked the ball over the line.
"We've been earning lots of wins lately and snatching draws from losing positions and we're heading into the final stretch of the season full of confidence," Madrid defender Nacho said postmatch.
"It's never easy to play here so we're very happy with the victory. Even though we conceded a goal from a set piece due to poor marking, I think overall we played well and were solid at the back."