An upgrade package introduced in Malaysia had a positive effect on the performance of McLaren's MCL32 in Friday's opening day of action in Sepang.
Fernando Alonso was third in the truncated FP1 session and fifth a few hours later in the overcast but dry second running.
The 1.1s gap between the Spaniard and team mate Stoffel Vandoorne was an indication of the impact of the upgrade which included anew floor and which was only fitted to Alonso's car.
"We trialed some new components on Fernando's car today, and they look to be a useful new addition," said McLaren racing director Eric Boullier.
"They perhaps also explain a large part of the disparity between drivers, as Fernando's package was slightly better suited to the characteristics of the particular circuit."
Alonso was buoyed by his day of work, underlining his trouble-free sessions and the efficiency of his car's set-up.
"We had a good day today. In the first session, we checked a few things on the car," said the two-time world champion.
"We went out when the track was a bit less wet and managed to put it in third position… which was nice.
"In the second session, on a dry track, the car continued to behave well, and we had no big things we need to change for tomorrow.
"We tried several different configurations, and they proved all positive, so we need to go through the data tonight to decide what to do.
"The car feels good on this circuit, with a lot of grip when using the Supersoft tyre.
"We missed some running due to the red flag at the end of the second session, but that happened to most of the teams. We’ll try to catch up with that work tomorrow in FP3, if it doesn’t rain."
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