Hamilton and Mercedes ended qualifying as the 'best of the rest' behind the dominant Red Bulls.
But in the race he lost out to the Ferraris and eventual winner Kimi Raikkonen's Lotus in the opening laps.
He later had to switch from a hoped-for two-stop strategy to a three, before coming back to fifth.
"I think it's great, I'm really happy," Hamilton said.
"I think it's way better than we probably ever expected in the first race of the season so it's a good place to start.
"We're going to have to go back and try and figure out why we were losing time to other people but I think the guys have done a fantastic job for us to have the pace that we did.
"The car was feeling really good so I don't really know how the other guys were pulling away so quickly but we will keep pushing and hopefully we'll get there eventually."
He admitted it was hard to understand how Mercedes had fallen back in the race.
"I just don't know where we lost out so we're going to have to go back and look at it," said Hamilton.
The second Mercedes of Nico Rosberg retired early.
"There was some cuts before and then just switched off," said Rosberg. "It's an electronic problem."
