Baxter, 27, has had more than 800 at-bats at the Triple-A level, and manager Terry Collins said Wednesday that he has shown a big league maturity far beyond his experience level.
Collins said that the Mets pegged Baxter in Spring Training as someone who might be a good pinch-hitter.
"There wasn't a lot of movement to it. It was pretty quiet, pretty short," said Collins of Baxter's swing. "Certainly, being a first-year player, I'm shocked about the job he's done. And it all goes back to how well he's prepared for his job. It's one of the most difficult jobs in baseball, for a guy who's been here, who's done it and knows the pitchers in this league. To do it as a rookie is remarkable."