Jenson Button has warned not to take his second place for McLaren in opening Spanish Grand Prix practice too seriously as he believes it was an anomalous result.
The Briton slipped back to sixth place in the afternoon session, and said his earlier pace was due in part to McLaren's very temperature-sensitive car finding the very narrow range of conditions that suit it.
"The afternoon was where we expected to be. This morning was good and we were quicker than expected," said Button.
"I don't think it's anywhere near as good as it looked in FP1.
"The hotter temperature this afternoon was a lot harder for us to get the car working in. We seem to have a very small temperature range. So on both the short runs and long runs, we were struggling more.
"This morning we looked a lot quicker maybe because of temperatures and fuel loads."
Button still believes McLaren has made some progress for Barcelona, predicting it will be in the fight to be fourth-quickest team.
"There are a few things on the car that I think help the balance and put us back into the fight with Force India and Williams, but everyone's behind Mercedes and we're obviously behind Ferrari and Red Bull," he said.
"The first three teams have big gaps between them and they're a lot faster than us. And that's a pity.
"There's more we can do overnight for long runs, but short runs look more tricky."