Magnussen had a more difficult qualifying at Sochi, going into it aware that he would have a five-place grid penalty for a gearbox change after final practice.
The Dane finished sixth overall, having been hampered by a fuel-flow sensor problem that forced him to turn his engine down.
"On the first run I made a mistake on my lap, and it was a one-lap run, so I just aborted the lap and came into the pits," he said.
"There were no problems with the car in the first run, we just made a mistake.
On the second run in Q3, we had a problem with the FIA fuel flow meter and had to turn the power down on the engine compared to Q2.
"So I was a little bit down on Q2 which explains some of the loss of pace."