Brandon Bailey had been to the Portland Expo before Thursday.

But this time he brought his wife and their two young children. This time he came not as an under-the-radar video coordinator with the Boston Celtics but as the head coach of the Maine Red Claws.

Bailey, 32, is the fifth head coach in the nine-year history of the Red Claws, Boston’s affiliate in the renamed G-League, which serves as a developmental platform for the National Basketball Association. He got the job in July but the team formally introduced him Thursday.

“This is something I’ve worked at for a long time, to have a chance like this,” said Bailey after first thanking Celtics Coach Brad Stevens, Danny Ainge, Boston’s president of basketball operations, and Bill Ryan Jr., owner of the Red Claws. “I’m extremely humbled and excited to get started.”

Bailey, who has never been a head coach at any level, follows the most successful coach in franchise history. Scott Morrison guided the Claws to three straight division titles and their first playoff win before earning a promotion to Boston as an assistant to Stevens.

Like Morrison, who grew up on Prince Edward Island, Bailey is the son of a coach. Mike Bailey is entering his 24th year at Saint Patrick High in Chicago, and has sent many of his assistants on to successful programs of their own.

“His dad is one of the best coaches in the state of Illinois, in the country, really,” said Doug Bruno, the longtime women’s coach at DePaul. “There are so many great coaches out in the trenches that you never hear about, and Brandon’s dad Mike is very special.”

As a 5-foot-7 reserve guard, Brandon didn’t receive any college scholarship offers. He went to DePaul and became a student manager for Bruno.

“What separated him,” Bruno said, “was that he knew he wanted to be a coach the second he stepped onto campus. He was nonstop about learning the game. He wanted to study every other coach’s offense, analyze it and understand why it worked.”

After earning his diploma, Bailey spent two years as a graduate assistant with the DePaul’s men’s basketball program, first under Jerry Wainwright, then under Oliver Purnell. In the summer he interned with Attack Athletics, the gym run by Tim Grover, who gained fame as Michael Jordan’s personal trainer. One the contacts he made there, Joe Boylan, was a recent Golden State Warriors hire after a stint as a video intern with the Celtics.

Boylan, now player development coach with Memphis, urged Bailey to apply for his old job, an unpaid internship, which is now forbidden by NBA rules. The Celtics hired Bailey, who had to wait until the 2011 lockout ended before getting started under Coach Doc Rivers.

“I learned a lot about pro basketball from Coach Rivers and what they were doing,” Bailey said, “but to be honest, I was trying to not get fired the first couple years. My head was spinning.”

There was the time, that first year, when Bailey was in a room with Rivers, Kevin Garnett, Paul Pierce, Ray Allen and Rajon Rondo, tallying stats from video of a recent game. In walked Ainge.

“I used to watch (Ainge) play against the Bulls all the time when I was a kid,” Bailey said. “He sits down and says, ‘Brandon, what do you think about this?’ At my age, and at my position, nobody had asked my opinion about anything. I just froze.”

Bailey learned from the experience. The next time Ainge asked, Bailey had an answer.

“Because of that, I always make sure I formulate an opinion,” he said. “I study what’s going on and why it’s happening, and why we do certain things. Sometimes (Ainge) might agree with you but he’ll take the opposite side just to see what you have to say.”

As Bailey grew more confident in his role, he earned more responsibilities. Stevens assigned him a third of the league for scouting purposes, and had him direct film sessions and install defensive coverages. Defense became Bailey’s niche. Now he gets to follow Morrison, who gained acclaim for his ideas on offense.

“I’m not going to be Scott,” Bailey said. “Scott did a lot of really great things here and was very successful. I’m going to make mistakes. There’s going to be times when I make a wrong substitution or call a wrong timeout or whatever.

“But as long as I learn from those mistakes, I think it will work out for myself and the team in the end.”