BOSTON — In July, Jordan Walsh clearly looked lost.

The rising second-year player with ambitious Summer League expectations was erratic on offense, inconsistent on defense and unreliable on offense. Even by the most optimistic interpretation, Walsh seemed miles away from becoming an effective rotation player.

When the 20-year-old reflected on his stint in Las Vegas a few months later, he admittedly thought the performance was “unacceptable.”

But things change very quickly in the NBA, especially at Walsh's young age. He spent the summer refining his game, simply following Jrue Holiday's advice slow. And he bought into the idea that he didn't have to force the issue on offense or demonstrate his depth of movement. He just had to get his act together defensively and do all the little things.

Joe Mazzulla noted Walsh's progress during training camp: “(He) defends at a high level, defends multiple positions, rebounds and then does well on offense. I’m really proud of his growth.”

Four months after Vegas, Walsh delivered the most significant minutes of his young professional career. He was the second player to come off the bench in a high-profile game against the Milwaukee Bucks and he made the most of his 13 minutes, earning rave reviews from his teammates and coaches.

“I thought Jordan played great,” Jaylen Brown said after the game. “His minutes were exceptional for our team. He grabbed some great offensive rebounds and had some great defensive possessions as well – but to his credit he was ready.”

Walsh played just over five minutes in the first quarter, missed two three-pointers, but held his own on both ends. The effort was enough to give Joe Mazzulla the confidence to turn to him again later in the game. Walsh came back into the game late in the third period and delivered. He scored late in the third period, drew a foul and made a big stop on Giannis Antetokounmpo.

It was immediately clear that Walsh had just experienced the most impressive minutes of his career. It's also evident that the 2023 No. 38 pick quickly rose to his spot in the rotation after playing just 83 total NBA minutes in his rookie season.

“Big game, big moment for a young player going against a potential playoff team,” Brown said. “I thought he contributed and helped win tonight.”

For a team as strong and flawless as the Celtics, simply contributing positively to a win is an accomplishment in itself; Joe Mazzulla has spoken numerous times about how difficult it is for young guys to break through and earn minutes

And the home crowd expressed their appreciation for Walsh's contributions, giving him a rousing ovation as he exited the game in the fourth quarter.

Joe Mazzulla, who has praised Walsh several times this year for his development, let the second-year player know his efforts were having an impact.

“I told Jordan that in the locker room – I think just figuring out a role and making big performances like that is huge,” Mazzulla said. “He had a great defensive play against Giannis in the post and took away his momentum – and he got fouled when he grabbed an offensive rebound.”

In just thirteen minutes, Walsh recorded a plus-minus of +10. His box score stats aren't outstanding – he had 3 rebounds and 2 points on 1-3 FG – but his contributions didn't go unnoticed by Mazzulla.

Entering this season, Walsh was one of several viable candidates for backup minutes on the Celtics' bench, a list that also includes Jaden Springer, Baylor Scheierman and even two-way player Drew Peterson. Walsh is two years younger than Springer and four years younger than Scheierman and Peterson and seemed more likely to be headed for another year in Maine.

On Monday night it didn't matter. When his number was called, Jordan Walsh was ready. He could also be ready for a significant NBA role.