Nico Rosberg admitted he and Mercedes had been surprised by Ferrari's superior pace in Sunday's Belgian Grand Prix.
The 28-year-old German said he had expected Mercedes to be slower than Red Bull, but not the Italians - whose Spanish driver Fernando Alonso finished second behind three-time defending world champion Sebastian Vettel.
"We expected to be a little slower than Red Bull, but we didn't expect Ferrari to be quicker than us," said Rosberg.
"That was a bit of a surprise, but we're going in the right direction. Solid is maybe the best way to describe it -- decent, but we didn't have the pace to go for the win today."
Rosberg added he felt he had the pace to have finished better than fourth, but had compromised himself in qualifying when he was outpaced by team-mate Briton Lewis Hamilton, who took pole, and finished third in the race.
"For me personally I had the race pace to do a bit better than I did," he said.
"I lost out a bit in qualifying yesterday and today with strategy a bit.
"It's always different when qualifying doesn't go well, (you're)always on the back foot a bit. I was giving everything I had, but it wasn't perfect - for me that would have been third.
"All in all it was OK though - still lots of points for the team, and we still have opportunities to get some great results."