Lewis Hamilton on his way to setting the fastest lap in the first practice session ahead of the 2018 Australian Grand Prix. Picture: Brandon Malone / Reuters

Melbourne, Australia - Lewis Hamilton led a Mercedes 1-2 at the top of the timesheets for the first free practice session at the season-opening Australian Grand Prix on Friday, while McLaren's hopes of a clean start were tempered by reliability issues.

Hamilton posted a flying lap of 1m24.026s on a glorious day at Albert Park's lakeside circuit, leaving a gap of over half a second to team-mate Valtteri Bottas.

Dutch wunderkind Max Verstappen was third in the standings for Red Bull ahead of Ferrari's Kimi Raikkonen. Four-times champion Sebastian Vettel was fifth for Ferrari, with home hope Daniel Ricciardo sixth for Red Bull.

After completing their installation laps, McLaren's former double world champion Fernando Alonso and Stoffel Vandoorne were confined to their garages for most of the session with engineers worried about an exhaust system problem.

McLaren, now powered by Renault engines after an acrimonious split with Honda at the end of 2017, was saved further blushes as Alonso finally emerged with 22 minutes left in the session to post flying laps and finish an encouraging eighth.

Vandoorne was 10th behind Renault's Carlos Sainz. Haas enjoyed a positive session with Romain Grosjean seventh.

Early signs are that the race to be 'best of the rest' outside Mercedes, Red Bull and Ferrari, will be tight early in the season, with little more than a second separating Grosjean from Force India's 16th-placed Sergio Perez.