Now in the midst of possibly the best season of his career and with the Marlins thinking playoffs, his attitude - and that of his teammates - has changed drastically.
Miami looks to stay hot as it hosts the opener of a two-game set with the Texas Rangers on Tuesday night.
The Marlins (62-62) just took three of four against Arizona with Stanton going 7 for 14 in the series to raise his average to .295. He hit his major league-leading 32nd homer in Sunday's 10-3 victory, and his four RBIs gave him a career- and NL-best 88.
"I think ultimately his numbers are going to speak for him when you talk about what he means to our ballclub and the intimidation factor that he brings to other ballclubs," manager Mike Redmond said. "This guy just continues to get big hits."
Stanton's stellar season has helped Miami match its win total from 2013, and it is just 3 1/2 games back of San Francisco for the NL's second wild-card spot.
"It's different to come to the field. It's not a morgue in here every time you walk in. I'm telling you, that's the way it feels when you're (losing)," Stanton said. "We're loose, we understand what's ahead."
Redmond has seen a major difference from last year's club, too.
"We appreciate where we are, and where we're trying to go," he said. "We've got to go out there and keep playing. This is a special group of guys who fight and battle. They pick each other up, and do all the things championship teams do."
After having Monday off, the Marlins send Jarred Cosart to the mound for his third start since being acquired from Houston at the non-waiver trade deadline.
Cosart (1-1, 2.92 ERA) allowed four runs in 5 1-3 innings of a 5-2 loss to Cincinnati on Aug. 1 before bouncing back to give up three hits over seven innings in a 3-0 win over St. Louis last Tuesday.
"I feel like I needed that (win against the Cardinals)," Cosart said. "Now that the nerves have subsided a little bit, I feel like I'm part of the team (and I'm) ready to keep building on that."
The right-hander, who is 10-8 with a 4.27 ERA in 22 starts in 2014, went 1-0 with a 6.00 ERA in two outings against the Rangers this season while with the Astros.
Texas will counter with Florida native Mike Mikolas, who will have plenty of support in the stands for this start. However, he hasn't been very impressive in his previous eight since being called up July 1.
Mikolas (1-5, 7.71) has given up at least five runs in half of those outings, including 10 and three homers over six innings of Wednesday's 10-1 loss to Tampa Bay.
The right-hander, who turns 27 on Saturday, knows he has to be better if he wants to be considered for a spot in the Rangers' 2015 rotation.
"I know I'm up here kind of on an audition basis for next year," Mikolas said. "I want to make as good an impression as I can. ... I've had my ups and downs."
So have the Rangers (48-76), who got a walkoff RBI single from Adam Rosales in Sunday's 3-2 win over the Los Angeles Angels to finish just 2-5 on their homestand.
"You think eventually we're going to pull one of these out," Rosales said. "(Sunday) was that day and it was fun. It was much-needed."