Jenson Button believes Mercedes is in a league of its own following the first day of practice for the Formula 1 season-opening Australian Grand Prix.
The Briton said he was surprised at the size of Mercedes' advantage, which he estimates to be around one second per lap over the rest of the field.
And while he downplayed his own team's practice pace, insisting second and fifth in the respective sessions had flattered McLaren, he said he had not anticipated rival outfits like Williams also trailing Mercedes by so much.
"We were two seconds off them [Mercedes] in the test and we're over a second off them [in practice] in the long runs," Button said after FP2.
"I think everyone's about a second off them, they're very quick.
"I don't think our outright pace is as good as it looks in practice but we're OK; our balance still isn't there.
"We're nowhere near the quickest, [but] it's a little bit surprising that [Mercedes is also] much quicker than everyone else, including the Williams - which looks a bit of a handful to drive in high-speed corners which is a surprise as well."
Button said that Mercedes' speed could also help it conserve fuel during the grand prix, which he feels will be a critical issue in Sunday's race.
"I don't know if other people [are having to] save fuel a lot but it seems we have to in the race," he explained.
"This is a very difficult circuit for fuel saving and using 100kg, so this whole race for us is going to be tricky with how much we have to back off.
"This is probably one of the worst circuits for fuel usage so it's going to be a tough one on Sunday.
"Outright pace is always [desirable], because if you have a quick car you can save fuel more easily - just back off more.
"At the moment we're reasonably reliable, engine's working really well, and our pace is alright.
"We're not as quick as the quickest cars but then we're a lot quicker than the slowest cars, so we're not in too bad a shape."