Lewis Hamilton has dominated the track during the first two practice rounds for the 2012 Formula One Petronas Malaysia Grand Prix, but his McLaren teammate Jenson Button had a harder time of it in the run-up to Sunday's race on the Sepang International Circuit.

It's been a good day for me. We've made a few changes to the balance of the car since the last race, and I'm much happier, Hamilton was quoted as saying at Formula1Blog.com after posting the fastest times in both of Friday's practice runs at Sepang.

Hamilton posted two first-place times of 1:38.021 and 1:38.172 on Friday's practice runs, leaving his teammate and Australian Grand Prix winner Button trailing with ninth- and third-place finishes on his practice laps at 1:39.323 and 1:38.535, respectively. Button was frustrated, particularly with the ninth-place run, because of difficulties with his car and the adverse conditions presented by Sepang.

The morning was a little frustrating: we had an oil leak which cut my session short, but it didn't really matter as the track was still dirty ... I think the race will be tough for all of us -- unless the circuit improves a great deal, there's going to be quite a few stops on Sunday, Button said.

Michael Schumacher and Mercedes are shaping up to be the biggest threat to McLaren's domination, as he posted the fourth- and second-fastest clockings on his laps, with times of 1:38.826 and 1:38.533, respectively. Schumacher's teammate Nico Rosberg was also harrying McLaren, posting third- and fourth-place times at 1:38.813 and 1:38.696.

We've had a decent start today at one of our home races here in Malaysia so I'm quite happy, Rosberg said, leaving little doubt about the team's outlook moving forward.

Lotus' Kimi Raikkonen is set to receive a five-place grid penalty at the race on Sunday due to an unscheduled gearbox change after Friday's practice sessions. Under 2012 Formula One regulations, gearboxes are required to last five races.

A bit more work for Kimi's crew this evening. An issue with Kimi's gearbox so we're changing it now, was the announcement Lotus made on the team Twitter account.

The gearbox problems leave Raikkonen's practice times indeterminate, and there's no telling what kind of time he might post during the third practice and qualifying rounds on Saturday now that he has a fully functioning car.

The sob story of the 2012 Formula One season so far has been HRT-Cosworth whose drivers posted double 23rd- and 24th-place times during the first two practice rounds. HRT's current times leave it just a hair outside of the required 107 percent of the leader time to qualify for the race. It remains to be seen whether the struggling team can kick it up another notch in the qualifier on Saturday.

Qualifying for the 2012 Malaysia Grand Prix is set for Saturday at 4 p.m. local time (4 a.m. EDT). The actual race takes place on Sunday at 4 p.m. (4 a.m. EDT).