American Louisa Chirico reached a career landmark, while Zarina Diyas was hampered by injury at the Citi Open.
Eighth seed Zarina Diyas exited the Citi Open in Washington with a suspected right arm injury, aiding local hope Lauren Davis in the process.
Diyas called for the trainer just five games into her clash with Davis at the WTA International hard-court event in the American capital, and eventually retired with the home favourite leading 7-5 2-1.
The world number 32 was competing for the first time since her run to the last 16 at Wimbledon, but she could not see out the contest - Davis being one of three Americans to progress to the second round.
Awaiting Davis in the last 16 is Monica Niculescu, the Romanian slicing her way past Lara Arruabarrena 7-5 6-4.
Davis was joined by Irina Falconi and wildcard Louisa Chirico in flying the locals' flag high.
Falconi downed compatriot and wildcard Taylor Townsend 6-7 (4-7) 6-1 6-3, while Chirico upended Briton Heather Watson 6-3 6-0.
For world number 128 Chirico it was no ordinary win, as it marked her first WTA Tour-level main-draw triumph.
Next up for Chirico is fifth seed Alize Cornet, who was largely untroubled against qualifier An-Sophie Mestach in a 6-3 6-3 victory.
Sixth seed Irina-Camelia Begu was too good for Madison Brengle 6-4 6-0, while Yulia Putintseva edged Kurumi Nara 4-6 6-4 7-6 (7-4).