NEW YORK — Late Saturday night, Celtics coach Ime Udoka sat in a lounge in the bowels of the Barclays Center that had been converted into an interview room for visiting teams, and he talked about Boston’s 109-103 win over the Nets that had given his team a commanding 3-0 lead in this first-round playoff series.
After about eight minutes, a team public relations representative indicated that the session had come to an end. Then Udoka realized it was because someone else was waiting.
“Mr. Williams,” Udoka said, smiling. “The man of the night.”
Celtics center Robert Williams was leaning against a chair in the back of the room, and as he walked toward the front he stopped and gave his coach a hug. It’s not often that a player who tallied 2 points and two rebounds would get this kind of reception, but the significance of Williams’s night went well beyond that stat line.
On March 27, the fourth-year big man tore the meniscus in his left knee during Boston’s win over the Timberwolves, instantly putting the team’s title hopes, which were gaining momentum by the day, in jeopardy.
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“[The surgery] wasn’t that scary,” Williams said. “I was just worried about the recovery process, how long that would take.”
There was some relief when it was determined that he could undergo the simpler of two possible procedures, likely sidelining him for 4-6 weeks rather than several months. But Boston likely would need to navigate at least its first-round series without him.
Even after the Celtics grabbed a 2-0 series lead against the Nets, Udoka publicly insisted that the team was expecting to be without Williams until the conference semifinals. But internally, the center’s progress was obvious.

“The first time I got on the court, I was trying to dunk, but they wouldn’t let me,” Williams said. “But the second time I got on the court, they let me dunk. And I felt like I was ready then. But I had some boxes I had to check off.”
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He took part in a few 25-minute scrimmages without any pain or issues, and the timeline was quietly shortened. After completing a workout prior to Saturday’s Game 3, he was cleared to return, just 24 days after his surgery.
Williams provides an instant boost to Boston’s top-ranked defense, but the jolt he gave to the team’s morale and greater aspirations might be even more significant. Anytime a player was asked about Williams on Saturday, both before the game and after, the response was preceded by a smile. They know what he means to this group.
“If we were going to do anything special this year, this postseason, we definitely need him,” All-Star forward Jayson Tatum said.
Udoka said before the game that Williams would be limited to about 20 minutes. Williams said he was slightly anxious when he checked in with 2:53 left in the opening quarter, but those feelings vanished quickly.
Thirty seconds into the second quarter, Williams rolled to the rim and received a lob pass from Derrick White. He took a slight shove from Brooklyn guard Goran Dragic before taking off, so the alley-oop dunk that followed did not count. But it at least put the Celtics at ease.
One minute later, Nets center Andre Drummond decided to test Williams in the post. He took two strong dribbles and made a move toward the right block before Williams jumped and erased his shot with little trouble.
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Two minutes after that, Tatum found him for another alley-oop, and this one ended up on the scoreboard.

“It was great to see him catch a lob,” Celtics forward Jaylen Brown said. “That was uplifting for everybody. Just his presence being there on the floor, knowing he’s behind us makes us feel good. And as we continue to go, we’re looking for him to continue to get his reps and come back strong and looking to make a push.”
Williams played 16 minutes and said afterward that he did not experience any pain. Udoka said Sunday morning that Williams still felt fine, and that he could have even played a bit longer than he did.
“My spirit has been great, just because after the surgery I was more mobile than I thought I’d be,” Williams said. “I was sad when I hurt myself and I was sitting on the bench because I knew something was wrong. When they told me four to six weeks, I just broke it down week-by-week in my head, and have just been grinding to get back.”
Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him @adamhimmelsbach.