The Canadian produced 17 blistering aces in the win over Del Potro, taking early control of the contest in Florida when he broke for a 4-2 lead in the first set after the Argentine went long on a backhand.
Raonic held serve comfortably to win the first set 6-3 but he faced a sterner test in the second set with Del Potro delivering some quality forehand winners.
The 26-year-old Raonic, runner-up at Wimbledon last year, broke to go 6-5 up in the second, only for Del Potro to break back immediately with a superb two-handed return down the line.
Raonic had earlier double-faulted at 30-15 when he was within two points of the match.
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The Canadian double-faulted again in the tiebreaker, this time at 5-4 up, but he held firm and won the contest with a trademark ace.
Raonic has beaten Sock eight times in 10 meetings but the American prevailed in their most recent match at the Shanghai Masters in October.
(Writing by Simon Evans; Editing by John O'Brien)
