It was a bad day for seeds at the Citi Open as defending champion Sloane Stephens, Eugenie Bouchard and Monica Niculescu bowed out in the first round.

Stephens was the biggest casualty in Washington before rain suspended play on Tuesday, the American second seed's title defence coming to an end at the first hurdle after being stunned by Risa Ozaki 6-2 6-1.

After reigning supreme in the American capital 12 months ago, Stephens was surprisingly swept aside in less than an hour.

Canadian fifth seed Bouchard was also eliminated in straight sets, going down 7-5 6-4 to Italy's Camila Giorgi.

Niculescu - the eighth seed - was no match for local Christina McHale in a 6-3 6-4 loss.

Puerto Rican third seed Monica Puig, however, did advance to the second round via a 6-2 4-6 6-3 win over Oceane Dodin.

Sabine Lisicki trumped Kristina Kucova 6-3 7-5, Naomi Brady was too good for Irina Falconi 6-3 6-4 and Tamira Paszek downed Lauren Albanese 6-3 6-4.

Meanwhile, fourth seed Kristina Mladenovic will return to finish her match on Wednesday following inclement weather.

Mladenovic won the opening set and trailed Samantha Crawford 3-1 in the second when play was called off, while Shelby Rogers and Lauren Davis were level at 4-4 in the first.

At the Bank of the West Classic, seeds Varvara Lepchenko and Jelena Ostapenko both crashed out.

Lepchenko - seeded eighth - lost 2-6 6-3 7-6 (7-4) to Alison Riske and Ostapenko was no match for Catherine Bellis 6-4 6-4.

Urszula Radwanska defeated Kateryna Bondarenko 6-4 7-5, Magda Linette saw off Kristyna Pliskova 2-6 6-2 7-5, Naomi Osaka lost to Julia Boserup 2-6 6-4 6-4, while qualifier Sachia Vickery upstaged Elitsa Kostova 6-1 6-2.