Ten years ago, when he was the rookie head coach of a young Orlando Magic team, Doc Rivers pulled one of his players aside and told him he’d be an NBA head coach someday.

The player wasn’t buying it.

“I thought he was crazy,” Monty Williams said Friday, a decade later. “It’s not what you’re thinking about. I’ve always focused on the task at hand. I just played hard and was worried about winning, and one day he just said, ‘Monty, you’re going to be a head coach someday.’ I was just like, ‘Where did that come from? What are you talking about?'”

But Rivers was right, and on Friday afternoon at the TD Garden, Williams suited up to coach his New Orleans Hornets against Rivers’ Celtics for the first time. The mentor was taking on the mentee.

Both coaches see the matchup the same way — they’re both competitive as ever and want to beat each other, but it’s a loving competition.

“Monty’s one of my favorite people in the world,” Rivers said. “He really is. I played with him in New York and San Antonio, I coached him in Orlando, and we’re very close. You knew right when he retired that he would be a coach. It was no secret with Monty.”

Rivers and Williams characterized their relationship as one of brutal honesty. It started early — when Williams broke into the league in 1994 as a rookie with the Knicks, Rivers was one of the team’s veteran leaders. He spotted the 22-year-old showing off with dunks in practice, and he quickly pulled him aside and chewed him out. “Work on your game,” he told him.

The years have gone by, but the dynamic hasn’t changed. Rivers continues to impart wisdom to the younger Williams, and he’s never been shy about it.

“He told me a lot of things, both when I was a player with him and for him,” Williams said. “He’s always been willing to take time to pour stuff into me that most guys wouldn’t in this league. He was the first guy to really pull me by the collar and adamantly tell me to work on my game because I wasn’t doing the right things, the things that would help me have a long career.”

The two remain close now, even as rival coaches. Their wives and children have solid relationships as well.

“To say he’s been like a big brother would be understating it,” Williams said of Rivers. “He’s been more than that. I hate to say I love him like a brother — I just love him. He’s just a great guy and he’s been a big part of my life for going on 20 years now.”