Harden finished 7 of 12 from the field, including 4 of 6 from behind the arc in 18 minutes - all in the first half. Harden had 15 points in the first quarter, including a 3-pointer at the buzzer to give Houston a 33-29 lead after one en route to a 61-53 halftime lead.
Patrick Beverley added 13 points and nine rebounds in 26 minutes, and Dwight Howard had eight points and four rebounds in 18 minutes - also all in the first half - to lead the Rockets (3-1) to their third straight preseason win.
Houston played without Jeremy Lin, who was sent home due to illness.
Reserve Manny Harris led the Magic (1-3) with 17 points on 8 of 16 shooting in 23 minutes. Andrew Nicholson finished with 15 points and nine rebounds, Aaron Afflalo added 13 points in 23 minutes, Maurice Harkless and Romero Osby had 10 apiece.
Orlando first-round pick Victor Oladipo struggled from the floor, scoring nine points on 3-of-12 shooting in 20 minutes as the Magic shot 22 percent from beyond the arc and 12 of 18 from the free throw line.
Donatas Montiejunas chipped in 14 points for Houston, Francisco Garcia had 11 and Terrence Jones added 10 for the Rockets, who shot 41.7 percent from behind the 3-point line and hit 23 of 27 from the free throw line.