WALTHAM, Mass. – Exactly one decade ago, the Boston Celtics embarked on their postseason journey to Banner 17. Ironically, the first successful steps of that playoff voyage came at the expense of a man who is now looking to lead the C’s to Banner 18.

Boston’s first-round opponent in April of 2008 was the eighth-seeded Atlanta Hawks, whose frontcourt was spearheaded by a young rookie named Al Horford. Showing great promise during his inaugural postseason experience, Horford helped the Hawks push the series to seven games, before the heavily-favored C’s finally prevailed.

It was the first failure that Horford had experienced on a basketball court in a long time, having won two consecutive NCAA titles at the University of Florida before entering the NBA. But that failure played a pivotal role in creating the leader that Horford is today – the leader that this year’s Celtics will count on to guide their young team to postseason success, starting Sunday with Game 1 of the first round against the Milwaukee Bucks.

“It personally shaped my career in the NBA,” Horford said Friday afternoon, looking back on the 2008 series against the Celtics. “For that (Hawks) team, it gave us a lot of confidence that we could play at a high level, and it really just taught me the intensity of the Playoffs, the way that you need to play.”

Facing off against the ’08 Celtics was the perfect way to introduce Horford to the postseason, because it showed him how connected and fundamentally sound a team needs to be in order to advance from round to round.

“That Celtics team was great because they were all about defending, they were really committed to helping each other and they knew their roles really well,” said Horford. “I learned a lot my rookie year playing against them.”

For one, Horford learned about the tools needed to build a championship squad. As good as his Hawks were, the Celtics were on a completely different level in so many areas of the game, and it was not only because they had a trio of veteran superstars guiding the way.

“I felt like we were over our heads going up against that Celtics team,” said Horford, who has not missed the postseason once during his 11 seasons in the league. “I felt like we pushed them as much as we could to Game 6, but at that point we were pretty worn down. I think that one of the things that goes unnoticed from that team was the depth that they had with their bench. Everybody always talks about (Kevin) Garnett, (Paul) Pierce and (Ray) Allen, but they had a lot of depth, and I think that’s what wore us down in the Playoffs that year.”

Horford was personally worn down by having to go up against Garnett in the frontcourt. The Big Ticket held no mercy for his rookie counterpart, testing Horford’s limits for seven straight games, before finally sending him home.

“He was a character,” Horford recalled with a laugh. “You know how he is. He’s out there screaming and just talking crazy on the court.”

Going up against Garnett also allowed Horford to understand the significance of home-court advantage at TD Garden, which the C’s will have at least through the first two rounds of the upcoming Playoffs.

“His energy, I felt like he fed off of the crowd a lot here at the Garden,” said Horford. “I just remember coming in here and it was like, coming in here, you knew you didn’t have a chance to win the game. But we’d just come in here, focused and trying to do the best that we could, because the fans here just have that extra grit, especially for the Playoffs. And that’s what was so fun.

“Now,” added Horford, “I’ve had a chance to be on both sides. And that’s one of the things that excites me most: Being able to play at home now that the Playoffs are starting.”

Horford will walk into TD Garden Sunday afternoon hoping to help the Celtics carry on their exceptional postseason tradition. His experience and knowledge of how to compete in the playoffs will be paramount to the C’s success, and that’s all thanks to the lessons the organization taught him one decade ago, while playing on this very same stage.