Ben Simmons' Philadelphia 76ers were dominated by the Toronto Raptors in their NBA playoff showdown while Patty Mills almost orchestrated a stunning season-saving comeback for the San Antonio Spurs against the Denver Nuggets.

The Raptors cruised past Philadelphia 108-95 on Sunday (AEST) in Toronto to strike the first blow in the best-of-seven games eastern conference semi-finals.

Three-time All-Star Kawhi Leonard had a career play-off high 45 points, 11 rebounds, two assists and two steals for Toronto.

The forward jumped on the 76ers early, with 27 of his points and seven rebounds coming in the first half.