Top seed Simona Halep survived to advance to the WTA Citi Open quarter-finals but Kristina Mladenovic and Eugenie Bouchard crashed out.
Halep rallied from a set down to prevail 3-6 6-4 6-2 against Mariana Duque-Marino in Washington on Thursday.
In sweltering conditions in DC, world number two Halep - who will meet seventh seed Ekaterina Makarova in the last eight - was forced to dig deep in a see-sawing contest lasting one hour, 40 minutes.
French second seed Mladenovic was not so fortunate, stunned 6-2 6-3 by teenager Bianca Andreescu.
Mladenovic was broken five times and tallied 10 double faults as she sensationally exited the WTA Tour tournament.
Bouchard's campaign also came to an end after she lost 6-2 4-6 6-0 to Andrea Petkovic.
Monica Niculescu trumped Patricia Maria Tig 6-4 7-6 (7-2), while Sabine Lisicki overcame Aryna Sabalenka 4-6 6-3 6-3.