FOXBOROUGH, Mass. -- One is widely regarded as a top -- if not the best -- quarterback of his era, while the other entered the final year of his rookie contract in 2012 without progress toward an extension.
One has a résumé that includes Super Bowl trophies and All-Pro selections, while the other seems to be perpetually fighting to earn league-wide respect.
Brady has more playoff wins as a starter than any other quarterback in NFL history, while Flacco made history of his own this postseason by becoming the first quarterback to start and win a playoff game in each of his first five seasons.
Their styles might be different, but since Flacco entered the league in 2008, their postseason results are comparable.
Their teams have faced off five times total -- Brady's teams have bested Flacco's on three of those occasions (although they've split two postseason matchups) -- but the Ravens signal-caller has stood toe to toe, throwing more touchdowns than Brady (9-5) and fewer interceptions (4-7).
Those results aren't lost on Brady.
"Joe has done a great job since he came into the league," Brady said of Flacco. "I've played against him a bunch of times, and he's always played really well.
"He's obviously a great leader," he continued. "You get your team to this position, it takes a lot of guys, but they have a lot of confidence in Joe. He does a lot of really good things."
Chief among those good things? Flacco can consistently drive the football down the field.
On Wednesday, before a reporter could even finish asking the question of whether the Ravens throw the deep ball down the field as well as any team the Patriots have faced this season, coach Bill Belichick delivered an emphatic "yes."
Flacco's unmatched arm strength was witnessed during the divisional round of the playoffs, when he threw three touchdown passes of more than 30 yards.
But while Flacco might surpass Brady in arm strength, the veteran Patriots quarterback is as cerebral as he is accurate.
He is a coach on the field for an offense that runs at a nearly unprecedented tempo, making checks and shifts at the line of scrimmage that affect all 11 Patriots on the play.
He fits throws into windows most quarterbacks wouldn't be able to see, much less dare to throw into.
Brady and Flacco play different brands of football. Their strengths vary, and the offenses they are asked to execute contrast starkly. But it is what they have in common that defines quarterbacks in the NFL: a track record of winning and leadership.
Their wins speak for themselves. No quarterback has more of them since 2008 than Flacco (61 total), while Brady is just 60 minutes from becoming the first quarterback to start in six Super Bowls.
As for their leadership, let their teammates explain that.
"Sometimes I look at him in practice and I say, 'Man, you have been doing this for so long and you are still worried about your footwork,'" nose tackle Vince Wilfork said of Brady. "But it is just little things, and he is always going that extra mile to make sure he is in the best shape and in the best situation and putting his teammates in the best situation that can give us a chance to win."
"He is still that guy that comes early and leaves late," added linebacker Jerod Mayo. "He is hard working, and even though he is a Hall of Fame quarterback, you would think this is his first year, that he was starting his first year in the league. That is the way he works."
"Joe Flacco is truly our leader," Ravens running back Ray Rice said. "Not only has he taken the role of our leader, he is leading us down this whole stretch. The one thing that he's doing is he is very vocal. He gets us lined up. He does everything that he needs to do as a quarterback.
"Everybody has a job," Rice added. "His job, obviously, is the hardest job on the field as the general, but we all have been taking parts, bits and pieces, and going out there and executing. Ray Lewis said it right. He is the general."
A current quarterback peer of Brady and Flacco's, Aaron Rodgers of the Packers, as well as Hall of Fame signal-caller John Elway recently echoed the sentiment that as an NFL player, you earn your paycheck during the regular season, but you make your legacy during the postseason.
The question was posed to Brady of whether he shares that belief.
"To tell you the truth, I don't really think about any of that," he replied. "I'm just trying to win a football game this week."
It's what Brady and Flacco have continually done over the course of their careers: win.
It is the thread that exists between the two quarterbacks who don't seem, on the surface at least, to have much in common.
They'll share the field this Sunday at Gillette Stadium, and something will have to give.