PHOENIX -- After missing nearly two months, Justin Upton is slowly getting back to his early season form.

Upton started out the season as the one of the hottest hitters in baseball, finishing April hitting .340 with five homers, 15 RBIs and a .962 OPS (on-base plus slugging percentage).

Then the 21-year-old rookie outfielder regressed quite a bit, hitting .216 in May and .123 in June with a combined four homers and 14 RBIs. After putting together a six-game hitting streak, Upton had to be placed on the disabled list after straining his left oblique during batting practice in Washington in July.

Since coming back from the injury, Upton has also come back to life, as he has hit .389 (14-for-36) since coming off the disabled list Aug. 29. On Sunday, Upton hit a 434-foot home run to left-center field, and Monday, he hit one almost to the exact same spot, 424 feet. On the homestand, Upton was 8-for-15 entering play Tuesday.

"He's riding a wave of confidence," D-backs manager Bob Melvin said. "We've all seen a very talented guy since the first day he's been here, since the first spring that he has been here at 19 years old. We know it's there, we know the ability is there. It's getting through the certain times of the season where you're struggling and trying to get confident like he is now.

"Whenever you're confident, swinging the bat well, it seems like every at-bat is not difficult to have a little bit better aura about you, a little better feeling when you go up to the plate. Right now, he's the one guy that every time he's up there, you feel like good things are going to happen."

Melvin has placed Upton third in the lineup the last two nights in games against the Giants, a spot in the lineup usually reserved for the team's most consistent hitter. Melvin said it could be a spot in the lineup that Upton will hit in the future, if he improves his walk total and on-base percentage.

"I think he's just more relaxed," Melvin said. "He's getting a better look at the ball. He's hitting breaking balls now, he's hitting fastballs away. He's hitting just about everything, which means he's seeing it and tracking it."