MELBOURNE - Lewis Hamilton and Nico Rosberg set the pace in practice for the Australian Grand Prix on Friday as Mercedes shaped as the team to beat at the much awaited season-opener. With teams adapting to a raft of technical changes in Formula One, Hamilton overcame mechanical problems in the first session to time quickest in the second run-out ahead of his team-mate. Ferrari's Fernando Alonso was third fastest while four-time defending world champion Sebastian Vettel, who endured endless problems in pre-season testing, placed an encouraging fourth."We got a nice foundation for the weekend in the second session today so hopefully we can build on that in P3 (free practice three) tomorrow afternoon and then see where we are in qualifying," said Hamilton, the 2008 world champion. "While it was disappointing to not get any track time this morning, we got up to pace quite quickly in P2 and found the balance relatively fast. I feel quite comfortable in the car so overall it's a positive start."The sessions were closely watched as the revamped cars, with new, quieter turbocharged engines and energy recovery systems, took to the Melbourne circuit for the first time. Hamilton and Rosberg have been tipped to fight it out in Sunday's race, given Mercedes' superior pre-season testing and adjustment to the technical changes, which also include a fuel limit.Hamilton put in a scorching lap on soft tyres to post a best time of one minute 29.625, some 0.157secs ahead of Germany's Rosberg (1:29.782). The Mercedes duo were the only drivers to go below 1:30, demonstrating an early edge over the rest of the field ahead of Saturday's qualifying for grid positions. Ferrari's Alonso backed up from topping first practice with the third best time of 1:30.132, just over a half-second slower than Hamilton.Defending world champion Vettel was fourth quickest in his Red Bull in 1:30.381, 0.756secs down on Hamilton but delighted to have completed 41 laps in his troubled car. "I'm quite surprised today, both Dan (Ricciardo) and I did a lot of laps so that's very good news, so let's see what tomorrow brings," said Vettel, who carried the initials of stricken great Michael Schumacher on his helmet visor."At the end of Friday times are not worth a lot but it is better to be closer to the top rather than somewhere lost in the back. In terms of speed we know there is a lot more to come but so far it feels very good." Earlier Hamilton had an inauspicious start to his 2014 season when his Mercedes stopped on its first lap of the first practice session, with smoke coming from the rear of the car. The Briton got out and the car was towed back to the team garage, in a setback for the Mercedes team.Hamilton, one of the sport's best known drivers, also had the indignity of having his pass checked by security as he returned to the paddock still wearing his race helmet. Mercedes reported that an oil pressure alarm had led to a precautionary shutdown in his car and Hamilton showed no problems in the second session. McLaren's former world champion Jenson Button had a promising day, finishing high in both practice sessions and clocking the fifth best time of 1:30.510 in the second run.Vettel's new Australian team-mate Ricciardo got in plenty of laps, 38, in the second Red Bull car and finished sixth. Alonso's new Ferrari stablemate Kimi Raikkonen was seventh, ahead of Finland's Valtteri Bottas in a Williams and Danish debutant Kevin Magnussen driving a McLaren. Japan's Kamui Kobayashi in a Caterham missed the entire second practice session after experiencing problems in the first session, meaning his whole day was wiped out. Pastor Maldonado also sat out the second session after problems with his Lotus, while Caterham's Marcus Ericsson only managed one lap in second practice.