"When I went to rehab in Triple-A [Reno], I saw him hitting and it was unbelievable," D-backs outfielder David Peralta said. "He was raking over there. And I told him, 'Hey, everything's about time. Everything's just time, just be patient, you're going to get a chance.'"
O'Brien got that chance when Arizona recalled him Friday and manager Chip Hale announced the 25-year-old would take over as the club's starting left fielder. He was batting .330 with 17 home runs and 52 RBIs at Reno, earning him his first opportunity at significant Major League playing time.
It likely won't all be easy as O'Brien transitions to face more challenging pitching. And it hasn't been easy thus far. He is 1-for-9 this year with five strikeouts, four of which have been on just three pitches.
Hale even decided to sit O'Brien on Saturday against Marlins ace Jose Fernandez, one of the top pitchers in the league. He may do the same when the D-backs face elite right-handed pitchers later on.
But O'Brien's power potential is evident, shown by his three-run home run in the first inning that went 424 feet with an exit velocity of 108 mph, projected by Statcast™.
"Guys are coming in throwing harder," O'Brien said. "I'm just trying to watch as much video as I can, talk to the older guys as much as I can, just to see what everyone's got. For the most part, this is my first time around seeing everyone. I'm going to be in here early every day and just try to get comfortable and have good ABs."
O'Brien, Arizona's No. 7 prospect as ranked by mlbpipeline.com, was a September callup in 2015. He went 4-for-10 with a homer, but played in just eight games and made only one start.
The D-backs are hoping this stint for O'Brien in the Majors, his first real chance to prove what he can do, results in similar numbers to those he had in Triple-A.
"That's part of the reason why we brought him up, it's instant offense," Hale said. "If he catches it on the barrel, there's a good chance it's going to go out."