ST. PETERSBURG, Russia, Oct. 29 (UPI) -- Top-seeded Mikhail Youzhny of Russia dropped out of the St. Petersburg Open in Russia Thursday, retiring with a back injury during his second-round match.
Youzhny was trailing Uzbekistan's Denis Istomin 2-6, 1-2 when his ailing back kept him from continuing.
A medical timeout did nothing to ease the pain and Youzhny, the 2004 St. Petersburg winner and last week's champion at the Kremlin Cup, decided he was done.
In another second-round match, former world No. 1 and retiring Marat Safin topped compatriot Igor Andreev 6-3, 0-1 when Andreev retired, citing a left knee injury.
Igor Kunitsyn defeated fellow Russian Michail Elgin 6-2, 6-3 and Ukraine's Sergiy Stakhovsky beat Russia's Andrey Kuznetsov 6-1, 6-4.
Friday's quarterfinal match-ups are Safin-Istomin; second-seeded Victor Hanescu-Kunitsyn; Stakhovsky-Bjorn Phau of Germany; and Horacio Zeballos of Argentina, the eighth seed, going against Latvia's Ernests Gulbis.