Leonard finished with 45 points and went five for nine from three.
However, the visitors were ultimately able to rally behind Leonard, whose dominance down the stretch included eight straight points in the final few minutes.
The five-time All Star made each of his five field goal attempts in the fourth quarter on his way to a 45-point performance.
Despite posting 29 points, eight rebounds and 11 assists, Doncic struggled from deep, scoring just two from nine beyond the arc.
Game seven takes place in Los Angeles on Monday.