Janowicz pasted Guillermo Garcia-Lopez 6-2, 6-1 in 58 minutes. Janowicz lost just nine points over his eight serving games and saved both of Garcia-Lopez' break chances.
Garcia-Lopez hurt his own cause with 10 double faults, which contributed to Janowicz getting four breaks and winning 52 percent of the points when Garcia-Lopez served.
Sixth-seeded Benoit Paire also moved into the quarterfinals, stopping Pablo Carreno Busta 6-4, 6-4 with two breaks in each set.
Fernando Verdasco eliminated No. 8-seeded Ivan Dodig 6-7 (2-7), 6-1, 6-4 in a first-round match. Jarkko Nieminen, with a 6-3, 3-6, 7-6 (7-3) decision over Benjamin Becker, and Kenny De Schepper, who beat Markus Eriksson 6-4, 5-7, 7-5, also claimed first-round wins Wednesday.
Swim Week Miami Beach 2014 [PHOTOS]