Lopetegui is rumoured to be on the brink of the sack at the Santiago Bernabeu after a dismal run in all competitions, but there was a timely victory for the reigning Champions League holders on Tuesday, albeit in unconvincing fashion.
While Plzen largely gave as good as they got, the recalled Benzema crucially broke the deadlock, scoring in a 14th consecutive Champions League season with a powerful early header.
A second from Marcelo followed, yet Patrik Hrosovsky pulled a goal back and Barcelona, Madrid's next opponents, would certainly have identified weaknesses ahead of El Clasico, which could have a huge bearing on Lopetegui's future.
Benzema provided a rare clinical moment in a first half packed with wasted chances, storming onto Lucas Vazquez's cross to open the scoring after 11 minutes.
Sergio Ramos had already nodded against the post and both Benzema and Isco failed to add to Madrid's advantage, the latter twice passing up opportunities inside the area.
There were clear openings at the other end too, though, with Plzen preying on Vazquez's poor positioning at right-back and going close on three occasions through Milan Petrzela, David Limbersky and Hrosovsky, who failed to hit the target with the goal gaping.
Jeers from the home crowd greeted missed chances at either end, the Madrid fans frustrated by their own side's profligacy and the ease with which their opponents marched forwards, while the early substitution of Isco was unpopular too.
Gareth Bale's flick teed up Marcelo for a dinked second goal to prompt some belated cheer in the stands, but Hrosovsky's long run and finish ensured a tense conclusion for both the supporters and Lopetegui, who would have been relieved to see his men claim three points.
What it means: A nervy few days for Lopetegui
Despite his pre-match protestations, Lopetegui must know he is in trouble. Some reports suggested the coach would be sacked regardless of the result against Plzen and, although his side won, this was not a performance that is likely to change many minds in Madrid. It is still not a given that Lopetegui will make it to Sunday's Clasico.
Benzema joins elite group with crucial goal
French forward Benzema netted in a 14th consecutive Champions League campaign on Tuesday. The only other two to achieve that feat? Lionel Messi and Raul. Dropped to the bench at the weekend, Benzema was wasteful at times against Plzen but his header at least eased the early tension.
Vazquez out of position and out of his depth
Lopetegui knew this was a game he and Madrid needed to win, but that did not necessarily mean the holders needed to go for broke. Selecting Vazquez at right-back was a strange choice and it very nearly cost the coach, his nominal winger exposed time and time again, rescued only by poor Plzen finishing.
Key Opta Facts
- Real Madrid have scored in each of their last 44 Champions League home matches, since a 2-0 loss to Barcelona in April 2011. Since then they have scored 127 goals at the Santiago Bernabeu.
- Vazquez has made more assists than any other Real Madrid player since the start of last season in all competitions (13).
- Real Madrid are unbeaten in their last 27 home Champions League group stage games (W24 D3), since a 3-2 loss to AC Milan in October 2009.
- Benzema is the fourth all-time top-scorer in the Champions League with 57 goals, surpassing Ruud van Nistelrooy (56).
- Madrid are the team with the highest possession figure (67% - level with Barcelona) and the most shots (77) in the Champions League this season so far.
- Federico Valverde has become the third Uruguayan player to feature for Real Madrid in the Champions League, after Carlos Diogo and Pablo Garcia.
For Madrid, it is the big one. With or without Lopetegui, they face Barcelona in El Clasico on Sunday. Plzen have slightly more modest opponents in the form of Slovacko this weekend.