The Canadian was playing his first match since losing to eventual champion Novak Djokovic in the quarterfinals of the Australian Open. He ran into a hot opponent in the 22-year-old Kwon, a South Korean who reached the quarterfinals for the second straight week.
No. 4 Ugo Humbert rolled into the quarterfinals by routing Marcos Giron 6-1, 6-0 in 51 minutes.
Also, No. 6 seed Miomir Kecmanovic beat Paolo Lorenzi 6-3, 6-3; and Andreas Seppi eliminated Steve Johnson 7-6 (4), 6-3.
Top-seeded John Isner and defending champion Reilly Opelka play their second-round matches Thursday.