Watson scored 19 points on 8 for 12 shooting as the Nuggets bounced back from a loss to the Minnesota Timberwolves.
The 19-year-old Watson also had seven rebounds, two steals and a block for the Cavs.
Gillespie shot 6 for 17, including 4 for 10 from beyond the arc, for Denver.
RJ Nembhard had 19 points on 7 of 13 shooting, while Cameron Young shot 3 for 9 and finished with 16 points for Cleveland, also with a 1-1 record.
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