Bursting onto the big league scene as a high-strung 21-year-old lefty with a wild high-kick delivery, Willis provided an instant spark to a Marlins team that was mired in mediocrity.
Willis' breakout rookie moment came on June 16, 2003, when the D-Train arrived in full force, turning in one of the best pitching performances of the season.
Matched against Tom Glavine and the Mets in Miami, Willis tossed a one-hitter, striking out eight in a nail-biting 1-0 win. A clean single to left by Ty Wigginton with one out in the fourth inning thwarted Willis' no-hit attempt. Wigginton was the only Met to reach that night. He also drew a two-out walk in the first.
The lone run, on a night where pitching prevailed, was Ivan Rodriguez's home run to right-center off Glavine in the seventh. The dramatic victory helped the Marlins gain more momentum in what turned into a championship year.
"I remember how excited we were in the locker room," Willis said in an interview recently with MLB.com. "All the guys. It was fun to be a part of that. I think that is when we started to turn it around and be one unit at that time."
In honor of Black History Month, MLB.com is looking back at great moments in team history.
Willis, now 30 and with the Phillies, was a driving figure on the 2003 Marlins, an underdog squad that shocked Major League Baseball by upsetting the Yankees in the World Series.
In many ways, Willis inspired the Marlins' remarkable turnaround. Shortly after the lefty was called up, the team fell 10 games under .500 in late May.
Willis was promoted from Double-A on May 9 and immediately made an impact. He became an All-Star, the National League Rookie of the Year Award winner and a World Series champion in his first big league season.
Tossing a one-hitter against Glavine and the Mets was an early indication that the young left-hander belonged.
"The one thing I remember about that game is Pudge was really vocal about me staying with him," Willis said. "I was following him the whole time. I didn't shake off a lot of pitches at all."
Rodriguez's home run may have accounted for the lone run, but Willis praised the veteran catcher's leadership behind the plate that June night.
"The knock people had on Pudge was his game-calling," Willis said. "But his game-calling, especially for the young guys not having a history with these hitters. He definitely took it upon himself, not just myself, but also for Josh [Beckett]. I think he took it personally. Once we started to roll, and he really started hitting to all fields, we were dangerous."
Willis called Rodriguez's opposite-field homer off Glavine, "Classic Pudge ... going to right."
"Once Pudge really turned into a field general and a leader, the rest is history," Willis said.
In 2003, Rodriguez was an established star with Hall of Fame-caliber credentials. That year, however, Willis became an iconic figure in a market looking for a baseball identity.
With his enthusiasm and fun-loving personality, he was an immediate fan favorite. D-Train mania swept South Florida, and Willis didn't disappoint on or off the field. He gave of himself away from baseball, devoting time to charity and community work.
"Like I've said for my whole career, I was blessed with great teammates, teammates who saw more in me than I did myself," Willis said.
One of his off-field initiatives in Miami was assisting underprivileged children by providing baseball supplies for sandlot leagues. Growing up in Alameda, Calif., Willis' first baseball experiences were on sandlot fields.
To this day, Willis' influence has rubbed off on not only the African-American community, but young people in general.
Last year, Willis was with the Reds, and he was a teammate of Aroldis Chapman, Johnny Cueto and Edinson Volquez.
"It's funny," Willis said. "I got to play with Aroldis Chapman, Johnny Cueto and Edinson Volzquez, who are phenomenal guys. They're talented. Way more than I am. They have way better stuff than I ever will have.
"The first thing they said to me, especially Cueto and Volzquez, was, 'We wear our hats the way we do because of the way you wear your hat.' At first, I took it personal, because I'm not that old. Then, it is really refreshing. Not only America, but internationally."
Willis has long sported a cap with the bill flat and tilted slightly.
"Now, you see guys wearing hats two sizes too big," Willis said. "Not only in African-American culture, you see it in the Little League World Series, as well. Wearing the flat bill with the sticker on it. It's really cool to be part of that."
Willis said he was inspired to wear his hat that way by former infielder Pokey Reese.
"That's who I got it from," he said. "He never got enough credit. He wore his hat like that. And J-Roll [Jimmy Rollins], back in high school, he wore his hat like that."
These days, Willis makes his offseason home in Scottsdale, Ariz., and he sees teenagers of all races wearing oversized hats with the flat bills.
"I'm in north Scottsdale now," he said. "Some white kids ran up to me at the Apple Store and started talking. They could barely see over their eyebrows with the hats they had on. I started laughing."