Josh Longstaff has plenty of great memories of the Portland Expo.

In 2000, there was the baseline jumper he sank over the outstretched arms of Jamaal Caterina to beat the buzzer and give Portland High a 50-48 victory over crosstown rival Deering in the Holiday Classic.

In early 2010, in his second season as head coach at Gorham High, there was the promotional half-court shot he swished at halftime of a Red Claws game to win $1,000.

On Sunday afternoon, with his parents and old high school coach in the stands, the 35-year-old Longstaff was hoping for another indelible moment.

And sure, he’ll remember looking across the court to see his parents, Tammy and Tim, among the crowd of 2,193. He’ll remember how perfectly his Erie BayHawks executed the alley-oop dunk from Josh Magette to Craig Sword to open the second quarter.

But the competitor in him will also remember that his team saw a third-quarter lead of nine points and a fourth-quarter lead of three slip away in a 102-96 G League loss to the Maine Red Claws.

“It was surreal for me,” Longstaff said afterward in the bowels of the Expo, having removed his blue suit jacket and purple tie. “The great thing for me was for our players to have the opportunity to compete in front of, to me, the best people in the world – the people of Portland, Maine, my family and friends.”

Longstaff landed this job with the Atlanta Hawks’ G League expansion franchise in July, after the New York Knicks let him go. He was a Knicks assistant for three years, coming over from Oklahoma City. The Thunder took him on as a video coordinator for player personnel in 2010.

He landed the Oklahoma City interview with help from a former assistant coach at Bryant University, where Longstaff walked on and became a four-year letter winner in basketball, and also pitched for the baseball team. That assistant, Brian Keefe, now works in player development with the Los Angeles Lakers after stints with the Knicks, Thunder and Spurs.

“When he was playing,” said Joe Russo, the Portland High coach who had Longstaff as a player for four years and an assistant for three, “I remember him saying, ‘I’ll be in the pros, some day.’ I’m thinking, he’s five foot eight, if that. All kids dream. It’s probably going to be unlikely, but you’d never tell anybody it’s not going to happen.’ But of course, as you know, there’s more than one road to get to the NBA.”

Russo spoke at halftime of Sunday’s game, as former Red Sox pitcher Bronson Arroyo strummed a guitar and sang Wonderwall.

“What makes him special is his people skills,” Russo said. “He just knows how to communicate and deal with people, and they like him because he’s genuine. I knew he’d be successful at anything.”

Three years as an assistant coach in New York also honed Longstaff’s sartorial game. On Sunday, he sported a high white collar, a form-fitting suit and fancy-looking black shoes. Brandon Bailey, also a rookie head coach with Maine, waved the white flag on that front.

“Listen, he’s big time,” said the more rumpled Bailey, who wore a checkered button-down shirt beneath a sport coat and no tie. “He’s been in New York, he’s been in OKC. He’s been in the (NBA) for a long time.”

Oddly enough, Longstaff’s parents both have ties to the Red Claws. Tammy owns Bayside Print Services, and Tim is president of National Distributors. Both companies are Red Claws sponsors.

“He’s so focused, so prepared,” Tammy Longstaff said of her son. “I think he’s having fun, too. What I’m most proud of, though, is that he has stayed so grounded.”

Indeed, Longstaff deflected much of the postgame talk toward his players. The BayHawks lost their opener in Grand Rapids on a buzzer-beater, despite 19 points and 11 rebounds from their best front-court player, Tyler Cavanaugh.

The BayHawks arrived in Portland on Saturday, and on the ride from their hotel to the Expo for practice, Longstaff received word that the Hawks were promoting Cavanaugh to the NBA.

“We were happy as heck for Tyler,” Longstaff said. “We announced it on the bus. We actually sent the bus back to the airport. That’s the second guy (from Erie, after Magette) that’s going to be able to play with the Hawks. We want that for all of our guys.”

As head coach, Longstaff has a say in travel plans. He decided another night in Portland would be a good idea, so the team won’t return to Pennsylvania until Monday.

The BayHawks play once more at the Expo this season, on Dec. 8. Longstaff looks forward to another night in the arena where his basketball odyssey began.

“It’s special for me to be able to come back here,” he said, before pivoting back to his players. “For them, it’s another game, another opportunity to get better. I don’t want to make it about me. It’s never about me. It’s about them.”