Seventh seed James Duckworth edged compatriot Alexei Popyrin in three sets, while eighth seed J.J. Wolf got past Stefan Kozlov in the San Diego Open first round on Monday.
Duckworth sent down 14 aces, winning 85 per cent on his first serve, and hit 53 winners as he got past Popyrin 7-5 4-6 6-1 in two hours and 20 minutes.
Popyrin could only manage 35 winners with 18 unforced errors. Duckworth will face one of the American qualifiers, Mitchell Krueger and Christopher Eubanks in the next round.
Wolf needed one hour and 52 minutes to topple countryman Kozlov 6-2 7-6 (8-6), converting three of his six break points, getting the edge by winning 50 per cent on Kozlov's second serve.
In the battle of the Argentines, Tomas Martin Etcheverry defeated Facundo Mena 7-6 (8-6) 6-3. Mena hit 28 winners but was undone by 23 unforced errors.
Frenchman Constant Lestienne fought back from a set down to win over American wild card Brandon Holt 5-7 7-6 (7-5) 6-3.