Dusseldorf - The United States fell to their second straight defeat at the World Team Cup on Tuesday, while Serbia posted their second victory in two matches.
The Czech Republic's Tomas Berdych and Radek Stepanek both won their singles in straight sets against the Americans. Berdych fired 12 aces in defeating Andy Roddick 6-1, 6-2 and Stepanek routed James Blake 6-2, 6-1.
Serbia also took an unassailable 2-0 lead over Russia.
Viktor Troicki lost only seven points on serve as he raced to a 6-3, 6-2 victory over Dmitry Tursunov. Janko Tipsarevic secured Serbia's victory by defeating Alex Bogomolov Jr. 6-1, 6-3.
Russia fell to 0-2.
Defending champions Germany made a winning start to their second Blue Group match as Florian Mayer dismissed Croatia's Ivan Dodig 6-1, 6-1.
Argentina took a 1-0 lead over Japan in a Red Group match when Leonardo Mayer defeated Japan's Tatsuma Ito 6-4, 6-4.