Points were free-flowing from both sides in the opening 12 minutes, as the Mavericks held a 35-32 lead after the first quarter.
The Thunder stayed hot in the second to take a six-point lead into half time. The back and forth trend of the game didn't change after the break as Dallas fought back to within a point with 12 minutes to play.
For the most part, the teams remained within one possession of each other, however the lead switched hands a number of times.
Westbrook was working the midrange game superbly in the final quarter, making Dallas pay for hanging off him on his way to a 38-point outing on 17-28 shooting.
With the time winding down, a momentum-building play where Adams somehow tipped a wayward shot in looked as though it might have spurred the Thunder on to a win.
However, Smith Jr took it on himself to silence the home fans and lead Oklahoma City with a win, htting clutch free throws and two huge three-point shots which proved enough to down he Thunder.
With the loss, the Thunder drop to a 20-16 record for the seaosn, but they remain fifth in the Western Conference.