The Briton recorded the fastest time at the Spanish circuit so far this year, finishing the day more than seven tenths of a second clear of his closest rival, Ferrari's Felipe Massa.
Although Hamilton has said in the past that he was not expecting to win a race this season, his car's form in testing has led to a change of mind, and he thinks that at some point a victory is now on the cards.
"I think we definitely will be able to win a race at some point during the season," said Hamilton.
"I hope we can, at least, but when that will be, who knows?"
He insisted, however, that there was no reason to get carried away about even loftier ambitions based on today's performance.
"I don't think it's anything you need to be impressed with really," he said of today's time.
"I think everyone's doing their own programmes and everyone's on different fuel loads so it's just another testing day for us."
He added: "I think it's important to bring everyone back down to Earth and realise that we've still got a lot of work to do.
"But Mercedes are doing a great job, both in the engine department and also with the car, it's obviously a lot better than it was last year."
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