(MENAFN- Kora) Stephens seeded fifth in charleston was trumped by ukraine's elina svitolina 6-4 6-4 in one hour and 25 minutes at the clay-court event.
Svitolina 19 is the highest-ranked teenager on the wta tour coming in at world number 35 and will face fellow youngster belinda bencic in the third round.
Bencic a swiss qualifier continued her impressive run with a 6-2 6-1 thrashing of new zealand's marina erakovic.
Bencic 17 is ranked 140th but has the chance to reach her first career tour-level quarter-final.
Keys the 15th seed at the wta premier event was bundled out by china's peng shuai 6-1 6-7 (3-7) 7-6 (7-4) in a two-hour 27-minute contest.
Peng's countrywoman zhang shuai was the day's other seeded casualty with the 16th seed falling to croatia's ajla tomljanovic 4-6 7-6 (7-4) 6-3.
Tomljanovic will face second-seeded serb jelena jankovic for a spot in the quarters after the world number eight thrashed american lauren davis 6-0 6-3.
Venus williams the 11th seed moved into the last 16 after she edged out south africa's chanelle scheepers 7-5 7-5.
Sabine lisicki the fourth seed from germany needed two hours and five minutes to dispatch of american vania king 7-5 4-6 6-3.
Lisicki's compatriot andrea petkovic was much more clinical thrashing spain's lourdes dominguez lino 6-0 6-0 in just under 50 minutes.
Third seed sara errani spent just 37 minutes on court with the italian leading qualifier kiki bertens 6-3 before the dutchwoman retired injured.
Slovakian 12th seed daniela hantuchova progressed with a 6-2 6-3 win over american qualifier grace min while 13th seed elena vesnina - of russia - came from behind to down czech petra cetkovska 3-6 6-2 6-4.
Legal Disclaimer:
MENAFN provides the information “as is” without warranty of any kind. We do not accept any responsibility or liability for the accuracy, content, images, videos, licenses, completeness, legality, or reliability of the information contained in this article. If you have any complaints or copyright issues related to this article, kindly contact the provider above.