Denver didn't trail again after Smith's bucket, which sparked the Nuggets' 117-105 rout Tuesday night that gave them a 2-0 lead in the best-of-seven series that shifts to Dallas this weekend.
"That was the key play of the game," Carmelo Anthony said. "He could've easily just let that ball go out of bounds, he chased it down, got J.R. the layup. We came down and we scored again and again and again. That play right there was the biggest play of the game."
Anthony scored 15 of his 25 points in the fourth quarter, including 10 in a 16-2 spurt the Nuggets used to start the quarter and break open a close game.
Billups said he never thought of just letting the ball go out of bounds or letting Terry beat him to it for a momentum-stuffing backcourt violation instead.
"Those are absolutely the kind of the plays you've got to make," Billups said. "If you don't make them, just try -- 100 percent effort. That play in a strange sort of way kind of turned the game around because it told us, that this is kind of game it's going to be.
"We can't really get away from these guys tonight. At that point in the game, we've got to make the extra plays, try to get extra possessions. That was a big play."
And it was deja vu for the Mavericks, who also collapsed in the fourth quarter of Game 1.
"I thought we were right there again like we were the other night and just things with this team can get out of hand quickly," said Dirk Nowitzki, who scored 35 points.
"They're so explosive. I think we kept the turnovers down but right there in that phase where they made their run, we had two or three costly ones and took two bad shots. The next thing you know, from a four-point lead it's 14. That's how explosive that team is. We've got to look at some stuff.
"It's a tough loss. We've got a while to sit on this one."
The series shifts to Dallas for Game 3 Saturday night, and the Mavericks can only hope they're going to be as good on their home court as the Nuggets were on theirs.
Nene scored 25, Smith had 21 and Billups 18 for the Nuggets, who won for the 15th straight time at the Pepsi Center, where they haven't lost since March 11.
The Mavericks are 17-1 at home since the All-Star break, but that one loss was to Denver.
The Mavericks now face the daunting task of having to win four of five against the Nuggets, a team they're 0-6 against this season and one that is playing with so much confidence and efficiency.
"They've held serve," Dallas coach Rick Carlisle said. "We go back to Dallas and we've got to do the same. We've got a few days to regroup and work on some things."
The Nuggets, whose six postseason wins have come by an average of 24.8 points, broke open a back-and-forth game by starting the fourth quarter on a 16-2 run, sparked by Anthony's 10 points, to take a 102-85 lead.
"We're just an explosive team in that way," Billups said. "That's just kind of what we do. That's who we've been all year."
Dallas didn't score until Brandon Bass's basket at the 8:36 mark, and then they went another 2½ minutes without another point until two free throws by Nowitzki.
After getting pushed around in the opener, the Mavericks said they had to stand up to the bullying in Game 2 and they tinkered with their starting lineup, replacing Jose Juan Barea with Antoine Wright.
They wanted to attack the rim more, but Josh Howard's two sprained ankles sent him to the bench after six scoreless minutes.
Kenyon Martin, who was slapped with a $25,000 fine for a hard foul on Nowitzki in the opener, was whistled for a double technical when he was grabbed by Ryan Hollins around his waist and tried to wrangle free. The Nuggets, who called the monetary fine overkill, also took umbrage at this whistle. ... Nowitzki, whose five free throws in Game 1 drew the ire of Carlisle, went to the line 13 times, making 12.