In 2005, Willis went 22-10 with a 2.63 ERA, becoming the only pitcher in Marlins history to win as many as 20 games in a season.
Willis also became the 14th African-American pitcher in Major League history to reach the 20-win plateau.
In recognition of Black History Month, MLB.com looks back at one of the most remarkable seasons ever by a Marlin.
At age 23 in 2005, Willis topped the NL in wins, complete games (seven) and shutouts (five). He was an All-Star, while also finishing as the runner-up to the Cardinals' Chris Carpenter for Cy Young Award honors.
"Just the domination that he had," said former Marlins outfielder Juan Pierre, Willis' closest friend on the team. "Everybody gravitated to him, even the guys on the opposing teams respected what he did. He was that good. They knew that they were in a dogfight when they were facing Dontrelle."
Pierre recalls conversations with opponents, who frequently said: "We're just hoping to get a couple of runs off him."
"That's how pinpoint he was that year," Pierre said.
Willis set the tone for his dominating season on Opening Day, when he threw a five-hit shutout against the Nationals. From there, he won his first seven starts.
"Everybody loved him," Pierre said. "We got up. The crowds got up. Even on the road, the crowds would come out and see him because he was the D-Train. He had the leg kick. He had so much charisma when he pitched. I think people gravitated to him, and the way he wore his uniform and his hat. It was something people weren't used to seeing in the big leagues, especially from a pitcher."
Now an MLB analyst with Fox Sports, Willis began his professional career as an eighth-round pick by the Cubs in the 2000 Draft. A native of Alameda, Calif., the Marlins acquired the lefty during '02 Spring Training.
It was an unpopular deal at the time in South Florida, because the Marlins parted with established big leaguers in Antonio Alfonseca and Matt Clement. In return, they received right-hander Julian Tavarez and three Minor Leaguers -- Jose Cueto, Ryan Jorgenson and Willis.
A year later, Willis burst onto the MLB scene, making the jump from Double-A Carolina to the Marlins after just six starts. The Marlins had a need in their rotation in 2003, and they saw enough in Willis' short stint at Carolina, where he posted a 4-0 record with a 1.49 ERA.
Willis was all the rage as a rookie, going 14-6 with a 3.30 ERA. But in 2004, he had a bit of a setback, finishing 10-11 with a 4.02 ERA in 197 innings.
The disappointment of 2004 was a driving factor in Willis bouncing back a year later, and making history.
Pierre, who trained in the offseason with Willis, could see the determination begin that November, months before the start of Spring Training.
"It started in November with his routine," Pierre said. "He was really focused on having a good year because of what happened to him the year before. He put in the work that led to that year.
"He had so much in '03 -- Rookie of the Year, the World Series. Then the next year, he didn't do as well. He refocused, and his preparation was unbelievable. You could see in his flat-ground work. With Dontrelle, if you put a challenge before him, he was going to figure it out."