Celtics fans exchange blows as fist fight breaks out during NBA Finals watch party at TD Garden after Game 4 blowout loss to Dallas Mavericks

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Several Boston Celtics fans brawled on Friday night at a watch party for their team, as tensions rose after Game 4 blowout loss to the Dallas Mavericks.

The Celtics had a chance to complete a sweep of the NBA Finals away from home but the Mavs extended the series with a 122-84 win.

And tempers flared at the Celtics' TD Garden as video showed blows being thrown by a fan in a Paul Pierce jersey.

The fan in the Pierce jersey knocked another fan in a green T-shirt to the ground and walloped him at least ten times as his fellow Boston supporter struggled to get to his feet.

In the midst of that, a fan in a zip-up hoodie grabbed the Pierce jersey-wearer from behind - seemingly to get him away from the other man - but he was punched by a friend of the man in the No. 34 jersey.

A Celtics fan in a Paul Pierce jersey delivered at least 10 punches to another fan on Friday

That fan was then grabbed from behind by another, who tried to get him off the other fan

The fighting spilled over to several other fans after the Celtics lost to the Mavericks

From there, security and other fans stepped in to try and deescalate the situation, though the drama was not over just yet.

The Pierce jersey-wearer yelled out that the man he was fighting was a 'p***y' 

And the fan in the green T-shirt was helped to his feet and began walking up the stairs with security, but then swung at a seemingly uninvolved fan.

Both men ended up on their backsides and the previously uninvolved supporter kicked out at the fan in the T-shirt. 

In Boston's loss to the Mavs - their first defeat in over a month - they struggled from the field and faced a 61-35 halftime deficit that the team couldn't recover from.'

Boston shot the ball horrifically in one of the most lopsided losses in NBA Finals history

It was one of the most lopsided blowouts in the history of the NBA Finals - with the 38 point defeat officially the third biggest point differential in a single game of the league's championship series ever.

Luka Doncic led the Mavericks with 29 points before being benched for the rest of the game late in the third quarter.

Meanwhile, Boston's stars Jayson Tatum and Jaylen Brown shot a combined 7-22 in a tough night for the Celtics duo.

The Celtics - and their fans - will have a chance for redemption on Monday as the series heads back to Boston for Game 5 and a potential championship.