The 35-year-old Spaniard, who won a record-setting 21st Grand Slam title at the Australian Open in January and lifted the trophy in Acapulco last month, stayed on track for a fourth title in the California desert.
But he had to weather a barrage of big shots from the 2.11m tall American, including a raft of serves that topped the 140 mph mark.
Nadal became just the second player to start a season 18-0 since the ATP Tour launched in 1990. Novak Djokovic has done it twice, starting 41-0 in 2011 and 26-0 in 2020.
The world number four next faces Australian Nick Kyrgios, who advanced on a walkover when scheduled opponent Jannik Sinner of Italy withdrew because of illness.
