McLaren's new Formula 1 aerodynamic upgrade package for the Malaysian Grand Prix encouraged racing director Eric Boullier, as Fernando Alonso finished fifth quickest in second practice.
Despite its struggles with engine supplier Honda, McLaren has consistently made improvements to its chassis throughout the season.
For Malaysia, McLaren brought a new package focused around the bargeboard area but only Alonso ran it.
"We're happy with the correlation of our parts," said Boullier.
"It's good to see new parts and significant parts that we brought here are reacting as we expected."
When asked if he was surprised by the pace shown by Alonso, he said: "Yes, it's a bit better than expected.
"He has a new package on the car and we also did a performance run, which I believe the other teams have not done this afternoon because there was rain this morning.
"As usual, it's practice - we don't want to be a champion of practice.
"We just do our own job and we are here to assess our own car and we do our own work."
There was only enough time to produce one update package, with Stoffel Vandoorne to get the upgrade for next weekend's race in Japan.
"We need to bring a significant amount of parts here," said Boullier.
"At every race, you need to cover the spares as well, and bargeboards are critical, especially when you run over kerbs.
"We have one spare and the plan is to upgrade Stoffel's car in Suzuka."
Alonso said it was a "positive" day but it was "early" to judge the success of the upgrade.
"In the first session we tried to test the car to see if everything was working well," he said.
"We probably went out when the track was less wet and we moved into third, which is always nice.
"In the second session the car was still handing well in the dry.
"We don't have big things to change for tomorrow so that's usually positive, so we'll see what we can do.
"Q3 will not be easy as usual, but we'll try to be there and see what happens.
"We have to analyse [the update] well tonight because every run I went out with a different configuration and it went well in the first, the second and the third."