The eighth-seeded Mikhail Kukushkin won his meeting with Teymuraz Gabashvili in straight sets, while Ivo Karlovic saw off Matt Ebden 7-5 6-4.
Benjamin Becker was a 6-3 6-2 victor against Lukas Lacko, Marcos Baghdatis saw off Rajeev Ram 6-3 6-4 and Jack Sock was too good for Adrian Mannarino over three sets.
Ryan Harrison was also a winner, getting the better of Bjorn Phau 6-3 6-4.
American Tim Smyczek came from a set down to beat Australian qualifier Nick Kyrgios 6-7 (5/7) 6-4 6-3.
In the final match of the day, Alex Bogomolov of Russia rallied to see off number six seed Sam Querrey 2-6 6-4 7-6 (9/7).