Fritz, the runner-up in this event last year, won without ever breaking Lu's serve.
Earlier Tuesday, qualifier Darian King defeated No. 5 seed Bernard Tomic 6-4, 6-4. King, ranked 140th in the world, dropped just 12 points in 10 service games against the 32nd-ranked Tomic.
Other winners Tuesday included No. 7 seed Steve Darcis, Ryan Harrison, Matthew Ebden and Tim Smyczek.
Harrison won 6-3, 7-5 over Konstantin Kravchuk to advance to a second-round matchup with No. 3 seed Sam Querrey. Darcis won 7-5, 3-6, 6-4 over Radu Albot. Smyczek beat Frances Tiafoe 6-3, 5-7, 6-3.
Ebden rallied from a break down in each of the last two sets to beat Peter Polansky 6-7 (4), 6-3, 6-1.