MIAMI -- In mid-August, when the Marlins' front office was deciding September callup candidates, Peter O'Brien was not at the top of its list. In fact, he wasn't part of the first wave of players who were promoted once rosters expanded on Sept. 1 -- instead, he was brought up on Sept. 4.
Now, the 28-year-old South Florida native who attended the University of Miami projects to be one of the frontrunners to enter Spring Training as the Marlins' everyday first baseman.
"I think Peter O'Brien is a very interesting player," Marlins president of baseball operations Michael Hill said. "He took full advantage of his opportunity upon being called to the big leagues. In his Minor League season, he hit over 30 home runs."
Initially, bringing up O'Brien from Triple-A New Orleans was an afterthought. At the time, the Marlins were hopeful that Garrett Cooper, recovering from a right wrist injury, would get about 100 plate appearances in September. But Cooper suffered a setback, and he ended up having season-ending surgery.
Martin Prado also was expected to play some first base in September. But the veteran infielder suffered a right abdominal strain, opening the door for O'Brien.

O'Brien made his mark in 22 big league games, hitting .273/.338/.530 with four home runs, five doubles and 10 RBIs.
The Marlins acquired O'Brien from the Dodgers' system on June 1 for cash considerations. With three Minor League clubs, the right-handed-hitting first baseman/corner outfielder combined for 30 home runs, 86 RBIs and 13 doubles in 2018. He opened the season at Double-A Tulsa before joining the Marlins organization, where he had stints at Double-A Jacksonville and Triple-A New Orleans.
O'Brien was drafted by the Yankees in the second round in 2012, and Miami's front office -- which has several former Yankees' executives -- has familiarity with his background.
A native of Hialeah, Fla., O'Brien grew up a Marlins' fan. He also spent 716 games in the Minors, with 161 home runs.
"For anyone who has followed him, he's a UM grad, local product," Hill said. "He has tremendous power."
Along with the long ball, O'Brien also has struggled making consistent contact, which was reflected by his overall Minor League numbers in 2018, when his slash mark was .216/.330/.505.
Still, the 6-foot-4, 235-pound O'Brien is a physical presence, and the Marlins plan on giving him every chance to show he could be a late bloomer and perhaps a big league regular.
The Marlins also saw a decrease in O'Brien's strikeouts after he was acquired from the Dodgers. In Tulsa, he had a 39.3 percent strikeout rate, and a 8.9 percent walk percentage. Once he joined Jacksonville, his strikeout percentage fell to 28.2 percent, and his walks increased to 16.1 percent. At New Orleans, the results were similar -- 29.6 percent strikeouts and 14.8 percent walks.
In September with the Marlins, his strikeout rate was 29.7 percent, and he walked at a 9.5 percent clip.
What really stood out for O'Brien, though, was his ability to impact the baseball. According to Statcast™, his average exit velocity was 92.1 mph, and his average launch angle, 16.5 degrees. His hard-hit percentage was 51.1 percent.
Granted, it was one month for O'Brien. By comparison, Justin Bour, Miami's regular first baseman before being dealt to the Phillies in August, had an average exit velocity of 88.7 mph and an average launch angle of 9.7 degrees for the entire season. His hard-hit percentage was 38.7 percent.
O'Brien also hit the ball harder this year than when he was last in the big leagues in 2016. Then in limited time with the D-backs, O'Brien had an average exit velocity of 86.2 mph, with an average launch angle of 16.2 degrees.
After finishing last in the Majors in home runs (128), doubles (222) and slugging percentage (.357), the Marlins will explore all their options at first base, and O'Brien is firmly in the mix.
"When you think about first base and profile the position, power is very important," Hill said. "We're going to look at internal candidates, and we're going to look at external candidates."