By Simon Evans
The Heat squandered a 15-point lead in the fourth quarter as the Mavs roared back to snatch the win, leaving the best-of-seven series tied at 1-1 with the next three games in Dallas.
However, Spoelstra was in no doubt his team would rebound in Game Three.
"No question about it, that's about as tough a fourth quarter you can have. When it started to slide, it just kept on going," said Spoelstra.
"Really, I think offensively if we could have executed and moved the ball, we might have been able to stem the tide a little bit, even as poor as we were defensively down the stretch. It was highly uncharacteristic for us on both ends of the court.
The Mavs went on a 17-2 run to tie the game, a spell during which Miami could not do anything right at either end of the court.
"So they probably scored eight to ten of those points on relief where our defense wasn't even set. And then we compounded that with a lack of execution. We will be much better in game three," added the Miami coach.
Spoelstra said he was confident that his team, who looked shell-shocked at the end of the game after Dirk Nowitzki's driving lay-up had sealed the Mavs' win, would have the character to recover in time for Sunday's game in Texas.
"We have found ways to respond under tough times, especially when we feel a great deal of pain, which are we are right now.
"We've been a very resilient group all season long. We've been tested. We've had our moments where we feel uncomfortable and feel like our backs are against the wall.
"That's when we've responded and been our best. We have a lot of guys who have some character and toughness to be able to respond to a game like this.
(Editing by Peter Rutherford)