"You can really feel that this new generation of car is much faster than last year," said Sainz after the end of Friday's practice session.
"I’ve done the fastest lap of my life around Melbourne this afternoon. And it’s only the second practice session!
"We still have more margin for improvement, but it’s already been very exciting to drive our new STR12," he added.
The cars are expected to be on average up to three or four seconds per lap faster this season. That's because of new tyre and downforce regulations that have been introduced over the winter. It's the first time the drivers have been behind the wheel since pre-season testing in Spain earlier this month.
"We were able to follow our programme, without suffering any issues, which was the main target for today," Sainz said. "We were able to keep learning and pick up from where we left in testing, so it was definitely a positive Friday.
"This doesn’t mean that we can now relax, as things usually get a bit more complicated on Saturdays, but it’s a good start."
Read the full article on eurosport.co.uk: Sainz hails 'fastest lap of my life at Melbourne'