At about 3 a.m., Thomas reportedly rebuked a fan, sparking an unfortunate confrontation inside the restaurant on the 4400 block of North Central Expressway.
Damien Pettie, 29, recognized Thomas, 32, and said, "What's Up?" according to police. Thomas responded by asking to be left alone, a request laced with profanity, racial and anti-gay slurs, police said.
Warning: Graphic Language: Read the unedited police report here to read the exchange between Thomas, Pettie.
Pettie responded to Thomas similarly and was promptly punched in the face twice by one of Thomas' friends, police said. The altercation quickly escalated into something reminiscent of an episode of Jerry Springer, complete with chairs being thrown and tables being overturned.
"He was there. His friend was involved," Mavericks owner Mark Cuban told ESPNDallas.com of Thomas' involvement. "We are being told that he was not a participant beyond having some dumbass friends."
KRLD-AM sports anchor Roger Emrich was at Denny's at the time of the incident and had a front row seat for the post-game scuffle.
"They landed on my table, broke my plate of food, and I'm thinking, 'I got to get out of there,'" he said.
He said a fan tried to strike up a conversation with Thomas, who "clearly didn't want to talk to this guy." Instead of letting it go, the fan moved to a table right next to Thomas and his friends, Emrich said.
"A couple of people from Tim's table got up and confronted this guy, and the next thing I know, one of the people with Tim threw a punch and hit this guy in the head."
But Emrich said Thomas wasn't involved in the melee.
"I didn't see chairs fly. There was one guy who was with Tim, picked up a chair and used it almost like he was trying to fend somebody off with it or maybe poke somebody with it," said Emrich. "As far as actual punches thrown or chairs thrown, or any of that, Tim did not engage in that."
A diner, Moya Kissick, was celebrating her 65th birthday with her daughter when she was struck by a flying chair she said was thrown by Thomas. Pettie later told the Dallas Morning News that Thomas was not the one who threw the chair.
Thomas and his entourage left the restaurant after the manager said he had called police. No arrests have been made in connection with the fight.
Mavs general manager Donnie Nelson said in the morning shoot-around that initial accounts of the incident are overblown.
"What I can tell you is that Tim was not involved,'' he said. "He's 30 years old with a wife and kids. When the situation started to escalate, he left the property immediately. Certainly we're working with authorities and our security folks to get to the bottom of it. But this is something that's way, way, way overblown. Innocent until proven guilty, last I checked."
Thomas, who was at the team's early Wednesday practice, is in his first year with the Mavericks and 12th in the NBA. He has played in 9 games for Dallas and averages under 8 points per game. He did not play in the Mavs' Tuesday night win over Phoenix.
When asked what discipline Thomas could face, Mavericks Coach Rick Carlisle said, "In our country, we have a model that says innocent until proven guilty. We should focus on basketball here."
Pettie was not seriously injured in the melee, though he did suffer a busted lip.
As for future visits to Denny's after a Mavs game, Emrich said, "Order your All-American Slam to go."