Nico Rosberg says he was surprised by the pecking order during practice for the European Grand Prix, with Force India and Williams emerging as Mercedes' closest rivals.
Lewis Hamilton led a Mercedes 1-2, as Rosberg's session was disrupted when his W07 Hybrid came to a halt in the final sector.
However, Mercedes was comfortably clear at the top of the standings, with Force India's Sergio Perez and Nico Hulkenberg its nearest rivals, the pair split by Williams' Valtteri Bottas.
Max Verstappen was the lead Red Bull driver in seventh, with Ferrari's Sebastian Vettel in eighth, a situation which came as a surprise for Rosberg.
"One lap pace was a bit tricky for me, as I only had one set of Soft tyres to use," he said.
"But on the long run with the Super Soft I was feeling good out there.
"Unfortunately my second session was a bit compromised this afternoon as I had to stop the car after I lost power. We are still investigating what happened there.
"I was a bit surprised by the order today, seeing Force India just behind us. I don't really know what to expect from Red Bull and Ferrari over the weekend, as they've been our closest rivals so far, so we'll see."