Daniel Ricciardo admitted that he was surprised by how far ahead of the rest of the field Ferrari's Sebastian Vettel ended up on Friday.
Vettel was more than eight tenths faster than the two Red Bulls in afternoon practice at Sepang International Circuit on Friday afternoon.
"Ferrari looked a bit stronger than we thought," Ricciardo said after the end of the day's track activity.
"We weren't that competitive, looking at Ferrari. But it looked like Mercedes struggled as well.
"We thought Mercedes would lead the pack and we would be a bit closer to Ferrari," he explained. "But Mercedes had a few issues today, by the looks of it.
"I saw some of Lewis's onboards and they looked like they were fighting the car. Maybe they are running 80kg of fuel. I don't know.
"We can focus on ourselves we can still improve," he continued. "On the short runs we needed to improve the front grip. And on the long runs we needed to improve the rear.
"We have just got to find a better compromise with the set-up. Just looking after that I think will be the key on Sunday. I think if we can find half a second somewhere then we’ll be in the fight
"We have still got a bit of work to do but we were okay," he insisted.
The morning session had been held under very different conditions. Intermittent rain and a wet track had made for a tricky time for all.
"We were looking pretty good in the wetter conditions this morning," said Ricciardo. "On the intermediates I thought we had the pace, significantly quicker than everyone else.
"If we get some light drizzle across the weekend then we’ll be looking pretty good," he smiled. "I won’t complain if qualifying and the race is wet!"
Red Bull's superior pace in the wet was proven by Ricciardo's team mate Max Verstappen topping the FP1 times. However it had been very much a lottery in terms of timing laps to hit the best available conditions.
“I think today was positive," said the Dutch driver. "Of course, compared to Ferrari it can be better. But it’s not a bad performance, and we still end the day ahead of Mercedes.
"I was trying quite a few set-up changes on the car [in the afternoon]," he revealed. "But those didn’t really work on the new set of Supersoft tyres.
"I still improved my time by four tenths," he added. "But I missed out on doing a long run this afternoon because of the red flag.
"I will see with Daniel how he is feeling, and then we will decide what we can do tomorrow to improve the car.
"For sure tomorrow it will be better but we still need to improve to beat Ferrari," Verstappen acknowledged. "I’m hoping for rain - not too much that we aren’t driving, but a little bit would make things interesting.”