MELBOURNE (Reuters) - McLaren's gamble on overhauling their car for the 2013 season looked to have backfired on Friday when they had a miserable day in the first two practice sessions at the Australian Grand Prix.

McLaren Formula One driver Sergio Perez of Mexico returns to the pit during the second practice session of the Australian F1 Grand Prix at the Albert Park circuit in Melbourne March 15, 2013. REUTERS/Brandon Malone

The British-based team won the last two races of last season but their cars were well off the pace at Albert Park with Jenson Button finishing 11th fastest in the second session - 2.386 seconds behind Red Bull's triple world champion Sebastian Vettel.

"We're 2.4 seconds off the pace, I'll be surprised, I'll be very happy if we're in the top 10," said Briton Button, the 2009 champion who has won three of the last four races in Melbourne and also won last year's season-ender in Brazil.

"It's definitely not the place where we wanted to start the season but all is not lost yet. We're very good at turning it round.

"I didn't think we were that competitive at the last test in Barcelona and I think I made that clear ... I still think we can improve the car a lot here."

Most teams were satisfied to bring out an evolution of their 2012 challengers in the final year of the V8 engines before sweeping changes to the technical regulations come into force for next season.

The British-based outfit, however, went down a different design route and produced a chassis with significant changes. Team principal Martin Whitmarsh admitted they had contributed to a difficult day.

"It was one of the hardest days I can recall," he said. "We were lacking overall grip, consistency, understeer, poor ride. Very difficult day when we didn't go forward during the day, which is bit of a worry.

"We made quite a conscious decision to make a lot of changes to the car for this season and we don't fully understand how to get the best out of it yet.

"But it's a long season, it's a choice we've made, it's a season that lasts from now to the end of November and we'll be developing the car throughout that period."

"It would be a lot more comfortable to start this season competitively and fight from there - we've done both in the past. It looks tough now but we're a tough team and we'll battle through."

McLaren lost 2008 world champion Lewis Hamilton to Mercedes at the end of last year and replaced him with Mexican Sergio Perez, who was 13th fastest on Friday.

Former technical director Paddy Lowe is also expected to join Hamilton when he leaves at the end of the season after 19 years at McLaren but Whitmarsh did not think his departure had an impact on the day's poor performance.

Whitmarsh stood by the decision to change the car, even if he admitted that last year's challenger would have been quicker on Friday.

"We felt that if we wanted to develop the car between now and the end of the season, we needed to make some changes," he said.

"There's a degree of risk in that but it was a judgement that we made. We still believe that we have a platform we can develop.

"We'll see later whether we're right or wrong."

(Editing by Alan Baldwin)

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