It was in May, however where Upton turned his season around, putting up 7 home runs, 21 RBIs, 8 doubles, 4 triples, a league-leading .709 slugging percentage, to go along with a .373 batting average and a .444 on-base percentage. On June 2, 2009, Upton was named NL Player of the Month of May by the MLB for his great month. His brother Melvin Upton, Jr. earned AL Player of the Month of June, making Justin and B.J. the first pair of brothers to win player of the month honors in the same year.
As of October 10, 2009, Upton led the Diamondbacks in batting average (.300) and hits (158) to go along with 26 home runs (including his first career grand slam on 6/2/09 against the Dodgers) and 86 RBI. He's also thirteenth in the NL in slugging percentage (.532, third among outfielders) and has compiled 20 stolen bases to go along with 7 triples and 30 doubles. On August 5, 2009 against the Pittsburgh Pirates, Upton strained his right oblique trying to steal second base, resulting in a stint on the disabled list. Rookie outfielder Trent Oeltjen had taken over his spot on the roster.
On September 1, 2009, against the Colorado Rockies, Upton was taken out in the top of the third inning after hitting a 420-foot (130 m) single in his previous at-bat. Thinking the ball to be a home run, he did not hustle to first base, and when the ball short-hopped the wall, he was forced to stay on first base.
In 2009, he led all major league outfielders in errors, with 12, and had the lowest fielding percentage among them (.961). Despite this, Justin Upton posted a 7.4 UZR, a statistic some believe to be more telling than errors and fielding%.