Dave Portnoy, on behalf of the Celtics, has finally surrendered.

The founder of Barstool Sports and passionate Boston supporter, who attended Game 5 on Wednesday at TD Garden, admitted in a video late in the third quarter that “I don’t think we’re coming back” before the Knicks secured a 119-81 victory.

“Hand up,” Portnoy stated. “You beat us. The Knicks beat us. I tip my cap. Knicks fans haven’t won anything in 1,000 years. Feels good to be a Knicks fan. And honestly, the Spike Lees, the Chambalambas, and the Ben Stillers who are true die-hard fans, they finally get their moment in the sun.”

Warning: Graphic Language

Portnoy had consistently believed that, despite lacking superstar Jayson Tatum and trailing 3-2 in their series, the Celtics could still find a path to advance to another Eastern Conference final.

He posted a picture on X earlier Friday wearing a Celtics shirt and holding up seven fingers, and before Game 6 began, he called out the fear he could sense in Knicks fans about their team’s ability to finish off the series.

“I’ve been on X a long time,” Portnoy wrote. “I’ve never sensed more fear and apprehension from a fanbase than I do from all Knicks fans right now. Pure fear. Pure terror. They are trying to put on a brave face on but I can smell blood in the water.”

Then, during the first half, Portnoy continued to post about positive developments for Boston — including how Kristaps Porzingis looked and the Celtics’ opening quarter — before his tone changed in the video recorded near the end of the third frame.

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By halftime, Boston’s chances of surviving the series were all but officially extinguished.

“The Knicks, they could beat anybody,” Portnoy said, who insisted the series would’ve been different if Tatum wasn’t injured.

“Brunson’s a great player. They have a great team. Not as great as us with Tatum, but they’re a great team. So bing bong. Bing bong. Congratulations to the Knicks. Bing bong. Bing bong. Bing bong.”

The Knicks got at least 20 points from four starters (Jalen Brunson, Karl-Anthony Towns, OG Anunoby and Mikal Bridges) as the Celtics’ blueprint without Tatum that worked in a commanding Game 5 win — a victory keyed by Derrick White and Jaylen Brown — struggled to materialize again.

The Knicks have now reached the Eastern Conference Final for the first time since the 1999-2000 season and a rematch with the Pacers, who beat New York in the second round last year.

The brutal loss left the Celtics — and Portnoy — staring down the end of their season, and what the next year could potentially look like without Tatum as he recovers from a torn Achilles.