Lewis Hamilton was forced to concede that Mercedes just didn't seem to have their usual dominant pace and power in Baku on Friday.
Hamilton was fourth fastest in FP1, and slipped to fifth in the later free practice session. More worryingly, he was eight tenths off the pace set by Red Bull's Daniel Ricciardo.
"Overall, we weren't quick enough today," he admitted. "Both Red Bull and Ferrari seem to be ahead of us at the moment.
"We've got some work to do. I'm going to be knocking on the doors of all the engineers overnight, so that we can hopefully make the right changes."
Mercedes' technical director James Allison was in agreement with his driver.
"We've got a lot more to do tonight in order to be able to take the fight to a very fast Red Bull," Allison said. "But we have plenty of directions to head in.
"It was a day of learning at this very unusual track [but] we've made progress," he insisted.
Hamilton's team mate Valtteri Bottas had topped the morning session, but in FP2 he was only just ahead of Hamilton.
"FP1 was better than FP2," the Finn confirmed. "I think we were missing a bit of pace in the second session compared to Ferrari and Red Bull.
"It's not an easy car to drive at the moment," he admitted. "We have some work to do with the balance.
"But if we get everything right, the car is quick," Bottas added. "We have plenty of things to look at tonight so that we make the right changes for tomorrow and Sunday."
Apart from the lack of pace, Friday had been a fairly decent time for Hamilton.
"It's been a smooth day," he said. "We got through everything we needed without many mistakes and we gathered lots of information.
"It started out quite warm but cooled down in the afternoon, which made it interesting to try and understand the tyres in both conditions."
However the weather expected over the weekend may yet turn the outlook for Azerbaijan Grand Prix on its head, as Bottas was keen to point out.
"The fact that we're here in Baku earlier than in previous years definitely affects the tyres," he said. "But the biggest concern is the wind.
"It's supposed to be very windy tomorrow and on Sunday which makes a lot of a difference on a street circuit."
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