Despite that, he has scored more points in the last three races than any other driver.
Asked about his title chances, Hamilton said: "It's too early [to talk about it] at the moment. [But] of course it's definitely in the back of my mind."
He added that he felt he had a car that was quick enough to win every one of the remaining races.
"I truly believe in this car. It feels awesome," he said.
Hamilton seals first Mercedes win
Hamilton struggled a little to adapt to the Mercedes car at the start of the season and was out-qualified by team-mate Nico Rosberg for three races in a row in Bahrain, Spain and Monaco.
But he is now getting to grips with it - the qualifying score after 10 races is seven-three to Hamilton - and Brawn said the Englishman would keep on improving.
"[Hamilton] is starting to pick up momentum and move in the right direction," Brawn said. "So we honestly don't know where the limit is, because we are on a journey with Lewis and we don't know where the limits are."
Brawn said: "It's our big challenge to maintain that [momentum]. Our hit rate [on developments] has been pretty good this season - things that we have brought to the track have generally worked and we've got some things coming up in the next few races that could give us the impetus and momentum to take us through the year."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.