Grosjean's 2012 campaign was littered with accidents as he developed a particular reputation for first-lap tangles, and the team hesitated over re-signing him for this season.
But the Frenchman has made a trouble-free start to 2013, finishing 10th in Australia despite a car issue, and then beating his Melbourne-winning team-mate Kimi Raikkonen to sixth in Malaysia.
Asked if he felt Grosjean's Sepang performance showed he had turned a corner in his career, Boullier replied: "I think you saw a strong Romain doing a good race.
"We know he has good pace over one lap so obviously it's about qualifying well and having a normal race condition.
"All the work he did is paying off. It's encouraging."
Boullier said Grosjean's disappointing 11th-place on the grid in the changeable weather of Sepang qualifying should be disregarded as the team was confident that in straightforward conditions he could now deliver more consistently.
"We know he has the raw pace. He would not be qualifying 11th normally," said Boullier.
"He can now run a complete weekend like we expect him to do."
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