Former Wimbledon finalist David Nalbandian beat Dominik Hrbaty for Argentina to level Slovakia in the opening singles of the Davis Cup semifinals on Friday.
The other semifinal between Croatia and Russia also was tied 1-1.
Argentina is playing in its third semifinal in four years, and trying to reach its first final since 1981. Slovakia reached the semifinals for the first time after beating last year's champion, Spain, and the Netherlands. Russia is the only semifinalist to have won the Davis Cup.
Nalbandian defeated Hrbaty 3-6, 7-5, 7-5, 6-3 after Karol Beck gave Slovakia a surprise early lead when he upset No. 8-ranked Guillermo Coria 7-5, 6-4, 6-4 with one break in each set on a hard court in Bratislava.
In Split, Croatia, Russia's Nikolay Davydenko beat Mario Ancic 7-5, 6-4, 5-7, 6-4, and Ivan Ljubicic, who plays his best tennis in Davis Cup, rallied to level the tie with a 3-6, 6-3, 6-4, 4-6, 6-4 win over Mikhail Youzhny.
Davydenko, who has never lost to a Croatian on the ATP tour, played above his own expectations against Ancic.
"It was probably the best indoor match I have ever played," he said.
Russia captain Shamil Tarpischev led the women to the Fed Cup title last weekend, and is trying to become the first person to sweep Davis Cup and Fed Cup titles in the same year.
In today's doubles, Slovakia's Beck and Michal Mertinak will face Argentina's Nalbandian and Mariano Puerta, and Ljubicic and Ancic meet Youzhny and Dmitry Tursunov.
Meanwhile, Roger Federer, Rafael Nadal and Andy Roddick -- the top three players in the world -- won in the World Group playoffs for Switzerland, 2004 champion Spain, and the US respectively.
In the playoffs, the winner remains in the elite 16-nation World Group, while the loser drops down to zonal play next year.
Federer did not play when Switzerland lost its first-round match to the Netherlands.
He returned for the tie against Britain in Geneva and overwhelmed 262nd-ranked Alan Mackin 6-0, 6-0, 6-2 on the indoor red clay.
Stansilas Wawrinka beat Scottish 18-year-old Andrew Murray 6-3, 7-6 (5), 6-4 in the second singles.
The US was in danger of being relegated from the World Group for the first time in 17 years.
The US team went 1-0 down against Belgium when Olivier Rochus beat James Blake 6-4, 7-5, 6-1 on the red clay at the Sportplaza in Leuven. Roddick made it 1-1 by beating Rochus' brother, Christophe, 6-1, 6-2, 6-3.
"It put a little more pressure on us," Roddick said.
Nadal only played the doubles when Spain crashed to Slovakia in March but, after winning the French Open, the 19-year-old has risen to second in the world.
Nadal beat Italy's Daniele Bracciali 6-3, 6-2, 6-1 after former world No. 1 Juan Carlos Ferrero was upset by Andreas Seppi 5-7, 3-6, 6-0, 6-3, 6-2 in Torre del Greco, Italy.
In other World Group playoffs it was: Austria 1, Ecuador 1; Chile 2, Pakistan 0; Czech Republic 1, Germany 1; Sweden 1, India 0; and Canada 1, Belarus 1.