Lewis Hamilton admits the Ferraris are "looking great", but feels there is plenty of room for improvement following his P1 at Sepang.
It was a mixed day for the reigning World Champion on Friday as he managed just four laps in the morning practice session due to an engine problem and was also forced to miss the start of FP2.
When he eventually emerged, he clocked only five laps before he was asked to return to the pits due to a telemetry issue. His team, though, managed to fix the problems and he went on to set the fastest time, a 1:39.790, with Kimi Raikkonen in the Ferrari second and Nico Rosberg third.
Although pleased that he managed to get out after such a long delay, Hamilton believes he still has some pace in the tank.
"Firstly it was just an amazing job done by my guys to rebuild the car and get the engine back on, and gearbox and everything, and get me back out," he told Sky Sports News.
"I'm very grateful for that. Particularly here where it's so hot it's so difficult for the tyres and everything, it was really important to get back out and do some laps. It affects you quite a bit. Fortunately I got a few laps of a longer run at the end, but in terms of my set-up I've not made any changes, so I've just driven what I have.
"It's quite a bit off with where I probably need it. I know my lap wasn't spectacular. As I said I think I've got some improvements I can make with the balance and the settings, they were all kind of brought from the last race. I'm sure we'll tweak it and improve it a little bit."
One team who caught the eye on Friday was Ferrari with Raikkonen second fastest in both sessions and his team-mate Sebastian Vettel P3 in the morning.
"The Ferraris look great, they really do," Hamilton said. "It's surprising to see how good their times are. We will see if it continues this weekend."
His team-mate Rosberg was also impressed by the Italian outfit and believes Mercedes need to watch out for them.
"It seems that again Ferrari is pretty close, so we need to keep an eye on them," the German said.