George Russell led the Silver Arrows charge with fifth place in Bahrain as team-mate Lewis Hamilton finished the season-opener in seventh, the pair having started third and ninth respectively.
Russell had climbed as high as second with an outside pass on Charles Leclerc on lap four to sit just 1.7s behind eventual dominant Red Bull winner Max Verstappen.
But his impressive start was undone by having to switch focus to nursing a power unit issue, which required lifting-and-coasting measures to combat rising temperatures. Hamilton was also hurt, further afflicted by a cracked seat.
The engine gremlins also disrupted power unit customer team Williams.
Both Alex Albon and Logan Sargeant suffered, with the latter additionally coming to a stop with a temporary steering wheel electronics fault.
Asked by Autosport to explain the reliability woes, Mercedes motorsport boss Wolff explained: "[Pre-season] testing was pretty good. Also, the performances on Thursday and on Friday were encouraging. The car was stable, was good. The drivers like it.
"When we started the race on the soft tyre, everything pretty much [was] to plan. And then, unfortunately, we had to start pulling the engine more than we expected. We can't understand yet where that came from.
"We have one of our customer teams, Williams, who had the same issue. The other two [McLaren and Aston Martin] not. That was unexpected."
Source: Autosport