The center fielder entered Sunday's series finale with the Red Sox on a nine-game hitting streak. Going into the game, he was batting .421 with two homers, four doubles and four RBIs during the streak, with six multihit games. In his first 14 games in May, Upton went 8-for-50.
Manager Joe Maddon has noticed a change in Upton's approach at the plate.
"He's more aggressive on pitches in the zone that he can really deal with," Maddon said. "He's more on time, and while he's doing that, I still think his strike zone is organized. But I like his mental aggressive approach to his at-bats, and that's what we're seeing as different."
For the season, Upton has a .303 average with four homers and 16 RBIs. The last time his average was this high this late in the season was on June 3, 2008, when he was hitting .307.
"He's definitely feeling better about himself," Maddon said. "He's hitting a wider variety of pitchers, and pitches also, which is good. He's on top of his game right now."
Upton's done it all for the Rays in their last three games. He picked up his fifth outfield assist of the year on Saturday, throwing out Dustin Pedroia at home. He had the fifth walk-off hit of his career on Wednesday, an 11th-inning double that beat the Blue Jays. On Friday he stole his ninth base in his last 14 games, and he leads the American League in steals, with 11.