As a 24-year-old in 2001, his second NFL season, Tom Brady stepped in when Drew Bledsoe was injured and led the New England Patriots into the playoffs.

When he arrived in Pittsburgh to play the Steelers in the AFC championship game, Brady couldn’t believe he was there.

“Fifteen years later, to be a part of 10 of those, I never imagined that any of this was even possible,” Brady said on Monday. “You never take it for granted.”

A sixth-round draft pick who spent his rookie year as the No. 4 quarterback on the Patriots’ depth chart, Brady has grown into a four-time NFL champion and a three-time Super Bowl MVP.

On Sunday, he will play in the AFC championship game for the fifth time in a row and the 10th time in his career, extending what was already an NFL record.

“It’s beyond what I’d ever imagined in my wildest dreams,” Brady said on his weekly radio appearance on WEEI.

Hall of Famer Joe Montana, whom Brady grew up in the Bay Area idolizing, played in seven conference title games, six with the San Francisco 49ers and another with the Kansas City Chiefs. He was 4-3; Brady is 6-3 heading into Sunday’s game in Denver against the Broncos and longtime nemesis Peyton Manning.

Patriots offensive coordinator Josh McDaniels said what’s most remarkable about Brady is his consistency. After playing in six Super Bowls in his career — and another 24 playoff games leading up to them — Brady isn’t likely to be overwhelmed by the moment.

“It’s a big football game, and he’s played in a lot of them,” McDaniels said. “Doing the things that you’ve done to get yourself in this position are really important. ... His preparation, his rest and treatment and getting his body ready and his mind right. He does a lot of the things every day to prepare for the next day.

“Even though these games have finality to them that some games in the regular season or preseason don’t have, he approaches it the same way.”

Brady is 22-8 in the playoffs, winner of his first 10 postseason games and his past four. His first career playoff loss and his most recent one were both in Denver, where he is 2-6 in his career.

The Broncos beat New England 30-24 in overtime on Nov. 29 — a victory that earned Denver home-field advantage for Sunday’s game. Manning was out for that one, replaced by Brock Osweiler, but he’ll be back on Sunday to face Brady in what could be his last game against Brady.

Although the two maintain a golf-and-dinner friendship in the offseason, Brady said he wasn’t sure if he would be in touch with Manning this week with such an important game looming.

“It will be fun to play another Peyton Manning-led team,” said Brady, who had a long run of success against Manning when he was with the Indianapolis Colts.

“It’s pretty hard to get to this point. There’s only four teams standing,” Brady said. “Two of these teams have to go home. Hope we’re not one of them.”