MELBOURNE  - World champion Sebastian Vettel took up where he left off last season as Red Bull dominated opening practice on Friday ahead of the weekend's season-opening Australian Formula One Grand Prix.Vettel -- bidding for a fourth consecutive world drivers' crown -- posted the fastest times in both practice sessions, settling with a best lap of one minute 25.908 seconds in the afternoon to stake his claim for Sunday's Melbourne race.Australian Mark Webber (1:26.172) completed an emphatic one-two for the champion Red Bull team as main title rivals Ferrari and McLaren trailed in their wake. "Overall it was a good day for us. It was pretty seamless and there was no trouble with the car," Vettel said."After all the mileage of testing, it was fun to be out there. This circuit doesn't get easier, it's a good challenge. Today was a good day and the balance was good, but we need to be ready for what's coming up."Ferrari's Fernando Alonso, edged out by Vettel in last year's championship, finished 0.840 secs behind Vettel's fastest lap, while last season's Melbourne winner Jenson Button was well down in 11th place in his McLaren. "Qualifying won't be easy, but I'm pretty sure we'll be able to do a better job on Saturday than we've done today," Button said.Team principal Martin Whitmarsh said McLaren were "struggling to understand" their new car and were lacking grip. "We were lacking overall grip, consistency, bit of understeer, poor ride so it was a very difficult day and we didn't go forward either, that's a bit of concern," Whitmarsh said."There will be a lot of data to be working hard and long on tonight and clearly it should be a base we can improve upon and we can do so tomorrow... it was a disappointing and tough day for the team." Alonso said he was not surprised by the quicker times recorded by the Red Bull cars."I'm not expecting any major surprises here, we already knew we were not the quickest and that was confirmed today," he said. "The car responds well, but we know there is still much to do if we want to fight with the very best." Vettel firmly eased doubts over Red Bull's performances in winter testing in Spain with his fast times as the Formula One season got underway.Coupled with Webber's speed in the team's other car Red Bull threw down the gauntlet to their rivals ahead of Saturday's qualifying for grid positions in the season opener. "We still have a huge amount to go through tonight and we're expecting a bit of overcast stuff tomorrow, so we need to be ready for that," Webber said. "Overall, it was pretty positive for us, but there are still areas to improve on."Lewis Hamilton, driving for Mercedes, clocked the seventh best lap time of 1:26.772 before his session was finished when he ran off the circuit near the end and was forced to walk back to the paddock. "Overall it was a good day, if perhaps not the smoothest," Hamilton said. "I'm happy with where we are and to see Nico in third place on the timesheets shows that we're pretty competitive."German teammate Nico Rosberg ran an encouraging third (1:26.322) for Mercedes but his afternoon session finished early with gearbox trouble. Former world champion Kimi Raikkonen was fourth in a Lotus ahead of French teammate Romain Grosjean.