Published: 2018-11-08 04:27:57 BdST
In temporary coach Santiago Solari's first Champions League game in charge Real began slowly but were out of sight before halftime after a masterclass of finishing.
Benzema opened the scoring in the 20th minute when he beat two defenders before slipping a shot through the legs of Plzen goalkeeper Ales Hruska.
Casemiro doubled the lead three minutes later when the Brazilian outjumped his marker and headed home from a corner.
An unmarked Benzema notched his second goal in the 37th minute with a redirected header assisted by Gareth Bale to give Real a 3-0 lead and Benzema returned the favour minutes later when he flicked on a cross for Bale to sweep home a volley.
Toni Kroos completed the scoring in the 67th minute when he cooly chipped over the keeper after a counter-attack involving Brazilian substitute Vinicius.
With two games remaining in Group G Real Madrid are in second spot, level on nine points with AS Roma who beat CSKA Moscow 2-1. CSKA have four points with Plzen on one.
Real had an early scare in the 10th minute when Patrik Hrosovsky's cross cannoned off Nacho and hit the woodwork.
But any hopes Plzen harboured of a shock win were wiped out with two quickfire goals in the 21st and 23rd minutes.
The hosts were more lively after the break and managed a few shots on goal but could not find the quality they needed in the final third to chip away at Real's lead.
Madrid beat Plzen 2-1 at home last month 2-1 with Julen Lopetegui at the helm before the former coach was sacked three months into his first season in charge after Real were thrashed by arch-rivals Barcelona.