Lewis Hamilton said McLaren's strong performance in qualifying at the British Grand Prix should act as a "wake-up call" to former champions Mercedes.
The seven-time champion and team-mate George Russell were seventh and sixth, but more than four-tenths of a second off the pace set by pole-man Max Verstappen in his Red Bull.
The defending double world champion and runaway series leader was fastest, two-tenths of a second ahead of McLarens' Lando Norris and Australian rookie Oscar Piastri, who were second and third.
"It's not a blow," said Hamilton, who has won the British race a record eighth times.
"It's just a wake-up call for us. Others have overtaken us and we need to do more."
Hamilton added that he expected it to be a difficult race for Mercedes and he anticipated struggling to beat the McLarens.
"Of course I'll try and be optimistic and we’ll do our best, but realistically, I'm not sure. We will find out. It was difficult to get past two Ferraris -- and then we've got two McLarens out there. It's going to be a tough race."
Hamilton also suggested that much of the heavily-updated McLaren’s big upturn in performance had come from producing aerodynamic parts that were very similar to the Red Bull cars.
"If you look at the car, it makes sense," he said. "I'm really happy for them. They've had such a bad run for so long so to be back up there is really, really great to see."
Hamilton began his Formula One career with McLaren and won his first title with them in 2008.
He added: "If you just put it alongside a Red Bull, it looks very similar down the sides and it's working. It is great. We now have another team in the mix, which is what we want to see in this sport."
Russell said that team data showed a big gap for Mercedes between their expected performances in qualifying and in Sunday’s race.
He said Mercedes had predicted they would qualify 17th and 18th, but had shown the pace to be third and fourth quickest in the race, on long runs, during the second free practice session.
"Our numbers suggest we were 17th and 18th in qualifying yesterday (Friday)," he said. "And third and fourth in race trim in FP2. So, clearly we’ve made some improvements.
"I was pretty gutted to see that we were only half a tenth from P3, which would have been incredible, but my lap felt great."
He praised McLaren for their success with their upgrades. "Well done to McLaren," he said. "They’ve come from nowhere and they're the big unknown for tomorrow… so let’s see."
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