Winston-Salem - Nikolay Davydenko's summer campaign stalled with a third-round loss at the Winston-Salem Open on Wednesday as third seed Alexandr Dolgopolov pushed through to the quarter-finals of the US Open warm-up.
Ukrainian ninth seed Sergiy Stakhovsky earned his first win against one-time top-five regular Davydenko, upsetting the 39th-ranked Russian fifth seed 6-4, 6-4.
Dolgopolov, who grew up as a toddler on the ATP as his father coached 1999 Roland Garros finalist Andrei Medvedev, needed more than two hours to hold off Bulgarian 14th seed Grigor Dimitrov, 6-4, 1-6, 7-6 (9/7).
Frenchman Julien Benneteau ended the run of Igor Andreev 2-6, 6-1, 7-6 (7/5) a day after the Russian clay-courter, ranked 79th, put out second seed Jurgen Melzer.
Davydenko, who has not been past a second round since winning Munich nearly four months ago, had been hoping to start building momentum for Monday's start of the US Open during this final preparation week.
But Stakhovsky put paid to that scenario as he advanced to the last eight with six aces and three breaks of the 30-year-old's serve to next face Benneteau.
Davydenko won their two previous meetings, spread between the first in 2004 and the second a week ago in the Cincinnati first round.
The winner will be playing in his third quarter-final of the season in a field headed by 21st-ranked Andy Roddick, who has been plagued by injuries and poor form in 2011.
Dolgopolov managed nine aces to 10 for rising star Dimitrov, with the winner moving into his seventh quarter-final of 2011.
American crowd-pleasers take to the court later, with Roddick playing Santiago Giraldo of Colombia and fourth seed, and local boy, John Isner taking on Finn Jarkko Nieminen.