He isn't the same short-tempered pitcher who took out his frustration in the dugout when things didn't go his way on the mound in Chicago. He isn't butting heads with teammates. He's no longer "El Toro," or "The Bull."
The difference: Zambrano is at peace with himself in Miami.
"He's happy, he's having fun and he wants to show people how good he can be," Marlins manager Ozzie Guillen said.
Guillen would know better than most. He and Zambrano have been longtime friends, and Guillen was instrumental in bringing Zambrano to Miami in January, when the team acquired him for Chris Volstad.
The move was a gamble for the Marlins, particularly after the way things ended for Zambrano in Chicago following 10-plus seasons with the Cubs.
After giving up five home runs to the Braves last Aug. 12 and subsequently getting ejected for throwing at Chipper Jones, Zambrano cleaned out his locker in the Cubs clubhouse and threatened retirement. The club suspended Zambrano for 30 days, and he later apologized to fans and teammates. The damage was irreparable though, and he was traded to Miami on Jan. 5, with Guillen leading the charge for the Marlins to land him.
But Guillen, who called Zambrano the Marlins' biggest question mark coming into the season, believes the move was best for all parties -- the Cubs, the Marlins and, most importantly, Zambrano. The pitcher said the move to Miami has been great for his family, and his relationship with Guillen, who called himself a bullfighter to Zambrano's "El Toro," has helped the smooth transition.
"Changing scenarios, I think that helped him," Guillen said. "It helped him in general. ... I think it was a good change for everyone, especially for him and his family. I think his teammates love him. I think he respects everyone. He plays the game the way he should be playing the game.
"Mentally, he's very clear. He's having fun and that's the main thing. He's got the big support from his teammates, his manager, his coaching staff, and I think that helps."
Zambrano has been, by all accounts, a model teammate in the Miami clubhouse this year. Mark Buehrle, who was in Chicago -- albeit on the South Side -- during Zambrano's tenure with the Cubs, said he didn't know Zambrano during those years, only speaking to him in passing and reading about him in the news.
But the Zambrano that Buehrle now calls a teammate isn't the same one who fought with teammates while with the Cubs.
"He's been exceptional," Buehrle said. "He's been a great teammate."
His attitude with the Marlins has been a marked improvement from last season in Chicago, when his relationship with teammates became permanently strained following the incident in Atlanta. His performance on the mound has significantly improved, too.
So far this season, Zambrano has been one of the Marlins' most consistent starters. Before an injury-shortened 2 1/3-inning outing against the Rays on Saturday, when Zambrano gave up seven runs prior to exiting with stiffness in his lower back, the righty sported a 2.81 ERA in his first 11 starts. The strong early-season performance comes as no surprise to Guillen, who predicted during the Winter Meetings that Zambrano would have a bounce-back year after going 9-7 with a career-high 4.82 ERA in 24 starts last season -- his fewest since 2002.
The turnaround Guillen predicted just happens to be coming in a Marlins uniform instead of a Cubs one.
"He's happy, and I think when you're happy where you're at and the situation you're in, that it helps," Marlins pitching coach Randy St. Claire said. "Things are going well for him and he's very content and very pleased with the way things are going.
"It's kind of, I think, a little bit of a new outlook for him."
Not only has the situation provided a new outlook for Zambrano and his family, but it has provided one for the Marlins, too.
In Zambrano's past eight starts, the Marlins are 6-2. They hope to improve on that record when he takes the mound in Friday's series opener in St. Petersburg, where Zambrano will look to bounce back from his last outing against the Rays.
When Zambrano was reluctantly pulled from the game in the third inning against Tampa Bay on Saturday, Guillen said the righty was understandably upset. Zambrano wanted to stay in the game and help his team, not walk out on them in a tough situation. But Guillen didn't want to risk losing Zambrano for an extended period of time.
After he handed Guillen the ball and walked off the mound with a trainer, Zambrano didn't take out his frustration on a water cooler, like he might have in years past. He didn't throw things in the dugout, either. Instead, he admitted afterward that he should've said something earlier about his back tightness -- before he put his team in an insurmountable seven-run hole.
"I always say if you got a tiger in a little cage and you let that tiger go, good luck [trying] to put [him] back in," Guillen said. "That tiger is not going to leave the cage as long as I wear this uniform. I am not going to allow it. Do I want Carlos to be upset, throwing stuff? Of course I want him to. I want the Carlos that has passion for the game, but I don't want the Carlos that's fighting with his teammates."
This Carlos -- the 2012 incarnation -- still has that passion. The only difference is now he's happy and focusing his energy on the field, not on distractions off of it.
Tom Green is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.