The Western Conference's top seeds lost the second fixture in their first-round playoff series, leaving them tied at 1-1.
The shooting guard told reporters: "They beat us in every aspect of the game. They played harder. Our defense was soft [and] not as aggressive as theirs.
"Not that I don't expect them to play hard. We know they are a tough team, but having such a poor performance in the playoffs bothers me."
The win was Dallas's first in the post-season since 2011.