Watson won the 2009 US Open junior singles title
British number three Heather Watson's Cellular South Cup run in Memphis ended at the quarter-final stage with a
6-3 6-4 defeat by Evgeniya Rodina.
The 18-year-old qualifier had won four matches to reach the last eight but was eclipsed by the Russian, who beat third seed Melanie Oudin in the second round.
Rodina served for the match at 5-3 but Watson delayed defeat by breaking the 22-year-old's serve.
But Rodina broke back immediately to seal victory in an hour and 39 minutes.
It was Watson's second quarter-final of the year, following her impressive performance in the Auckland Open in January.
The match against Rodina featured nine breaks of serve.
Meanwwhile, in the men's tournament, the Regions Morgan Keegan Championships, top seed Andy Roddick and defending champion Sam Querrey eased into the quarter-finals.
Roddick, a two-time Memphis champion, survived set points in the second-set tie-breaker before overcoming Serbia's Janko Tipsarevic 6-1 7-6 (10-8).
While fellow-American Querrey beat Argentine Brian Dabul 6-3 7-6(7-3).
Other winners were Juan Martin del Potro, Lleyton Hewitt and Milos Raonic.
Canadian Raonic, the 20-year-old winner of last week's SAP Open in San Jose, blasted 38 aces on his way to winning against Czech Radek Stepanek 6-4 6-7 (10-12) 7-6 (7-1).
Argentine Del Potro beat Croatia's Ivan Dodig 6-4 6-4 while Australian Hewitt recovered from losing the opening set to finally come through against Frenchman Adrian Mannarino 6-7 (9-11) 7-5 6-0.