Given time to reflect on his comment, Harbaugh didn't back down.
"I said it. I meant it," Harbaugh said after Tuesday's practice.
Flacco's numbers in the postseason support Harbaugh's lofty assessment.
After throwing two touchdown passes in a 30-17 win over the Steelers, Flacco improved to 5-0 in his last five playoff games. He has 13 TDs, no interceptions and a 116.6 quarterback rating during that span. He was Super Bowl MVP two years ago, is 10-4 in the postseason and has more road playoff wins (seven) than any quarterback in NFL history.
Flacco has twice as many playoff wins as peers Drew Brees, Aaron Rodgers and Ben Roethlisberger.
So, is this guy elite or what?
"At the end of the day it doesn't really matter what everybody wants to think," Flacco said. "It obviously means a lot for a head coach to stand up in front of everybody in the whole world and say those kind of things. Whether it really means anything, I don't know. But it definitely means a lot to me."
Harbaugh became Baltimore's coach in 2008, the same year the Ravens made Flacco their top draft pick out of Delaware. The two have been to the postseason in six of seven years.
"Joe has a great arm, is a very good athlete, a big, strong guy in the pocket, can make any throw in any kind of weather," Harbaugh said.
Especially in the playoffs.
"He's a good quarterback, period," said New England coach Bill Belichick, whose top-seeded Patriots (12-4) host the Ravens (11-6) on Saturday.
"I have a lot of respect for him," Belichick said. "He has a great arm, can throw the ball the length of the field with guys hanging all over him. He's mobile. He's athletic enough to extend plays, makes good decisions, uses all his weapons."
Flacco and the Ravens beat the Patriots 28-13 in the AFC championship game two years ago to advance to the Super Bowl. Flacco joined Joe Montana as the only quarterbacks in NFL history to throw 11 touchdown passes without an interception in a single postseason.
"Big-time players show up when you need them most, and that's how he's been," Ravens fourth-year receiver Torrey Smith said. "He's as good as anyone, and maybe the best in the playoffs these past few years."
Soon after Baltimore beat San Francisco 34-31 in the Super Bowl, Flacco received a contract worth $120.6 million that made him the highest-paid player in NFL history.
To this point, it's been a worthwhile investment. Although the Ravens went 8-8 and missed the playoffs last year, they've never had a losing record and are 82-44 (including the postseason) with Flacco as a starter. Oh, and he's started every game since the outset of his rookie year.
Flacco has thrown 166 passes in the playoffs since his last interception, in the 2011 AFC title game in New England.
"I'm doing the best I can to put everybody in position to do good things," he said. "Put the ball in their hands and let them take over."
Flacco is 6-foot-6 but surprisingly agile in the pocket. Against Pittsburgh, he scrambled to his left to elude the rush and threw off his back foot to connect with Smith for an 11-yard touchdown that made it 20-9.
"His athletic ability is underrated," Smith said. "He's been making plays like that for a long time."
In the playoffs, though, something special happens when Flacco is on the field.
"He's a franchise quarterback and has had a great career," Patriots quarterback Tom Brady said.
Brady is among a select few top-shelf quarterbacks considered to be the best in the game by those not named John Harbaugh.
"The cool thing about it is, Tom was playing for who knows how many years before I got in here," Flacco said. "I was in high school watching him win Super Bowls."
Flacco is 2-1 in the playoffs against the Patriots, but warns that those games — and this one — aren't about Brady vs. Flacco.
"It's not really me outdueling Tom or him outdueling me," he insisted. "We're not playing against each other."