Carlo Ancelotti’s side are 12 points behind La Liga leaders Barcelona.
The Frenchman curled in his second from another Vinicius pass and then scored a close-range overhead kick – with Asensio and Lucas Vazquez also netting.
It was the fastest Madrid hat-trick in a La Liga game since Fernando Hierro’s three goals in six minutes in a 7-0 win over Espanyol in April 1992.
Rodrygo, who set up Benzema’s third goal and Asensio’s strike, had another finish ruled out by the Video Assistant Referee (VAR) for a Vinicius handball and struck the woodwork too.
Valladolid, who are just one point above the relegation zone, hit the post in each half through Roque Mesa and Kike Perez.
It was a morale-boosting win for Madrid, who are practically out of the title race, but face Barca on Wednesday in the Copa del Rey semi-final second leg.
Boss Ancelotti was able to bring off key players including Benzema and Vinicius and introduce some players who have barely played recently including Eden Hazard.
The Belgian, making his first La Liga appearance since September, set up Vazquez’s injury-time goal.