But on Saturday, these longtime colleagues and good friends will go head to head. Dantonio will make his Division I head coaching debut as Cincinnati visits Ohio State (12:10 p.m., ESPN-Plus).
Tressel admitted he is not crazy about this scenario, although he is certainly ecstatic over Dantonio's good fortune.
"I think those things are difficult," Tressel said. "While you love to compete against your brother, it's tough to compete against your brother. He knows that we're going to root for him like crazy, just like he's going to root for us like crazy. But yet, the first time we tee it up, the last thing we'll be doing is root for each other.
"That's difficult. It will, I'm sure, heighten the awareness within our team of how good they're going to be because they know how good he is. They know how good (UC assistants) Mark Staten and Jeff Uhlenhake and Mike Tressel and Dave Andrews and all the people who were with us last year who are with them this year. Not to mention their 23 starters or whatever it is they have back. It will be a great challenge. But it's still a happy thought that he got a head coaching opportunity."
When Tressel took the OSU job in January 2001, he immediately brought Dantonio in from Michigan State to serve as his defensive coordinator. And the two of them, almost as quickly, made a beeline to Canton to meet with defensive back prospect Dustin Fox, who was wavering between OSU and Penn State.
Of course, Fox was taken by OSU's new dynamic duo. He signed with the Buckeyes and played three seasons under Dantonio's tutelage. Now, as one of the OSU captains, Fox also admitted that this scenario is interesting, to say the least.
"It is kind of funny how things work out," Fox said. "I love Coach Dantonio. He is one of my favorite coaches and he was one of the reasons I came to Ohio State. But for him and his family, he did what he had to do to get where he wants to be. We still talk on the phone.
"On a personal level, I wish we did not have to play them in the first game. After the game is over, I'll be happy for him. I'll root for Cincinnati. I love him. I love him and his family. They're great people."
OSU linebacker Mike D'Andrea confirmed that the Buckeyes will be all business when they line up against Dantonio's Bearcats.
"We have respect for him and his family and for everything he did for us," D‘Andrea said. "But we are going to go out there and try to beat him. He'll have an edge in knowing our personnel. He knows what our people can do and what our defense can do."
OSU defensive tackle Marcus Green was initially recruited by Dantonio to MSU. Then, after his move to Ohio State, Dantonio came back at him with an OSU shirt on.
"He recruited me, but I don't know that it's going to be any different," Green said. "I'm just going to try and go out there and beat Cincinnati. He's my enemy now. In high school, I used to have to play against my father's team. That was no different. He was the enemy."