MADRID, Spain (AP) — Sam Querrey always knew his Davis Cup debut was going to be difficult. But this is as rough as it gets.

The 20-year-old American will face top-ranked Rafael Nadal in today's opening singles of the Cup semifinal against Spain. The match will be played on Nadal's favorite surface, clay, before a capacity crowd of 21,000 in the Las Ventas bullfighting arena.

No. 8 Andy Roddick faces No. 5 David Ferrer in the other singles on the first day of the best-of-five format.

"Either one of those guys, Rafa or David, they're unbelievable players," said Querrey, a last-minute substitute for James Blake.

"So either way it would have been a tough debut, but it'll be a good starting point for me whatever happens."

Spain is an overwhelming favorite to reach its sixth Davis Cup final. The reigning champion U.S., which has won a record 32 Davis Cup titles, was left scrambling following the withdrawals of Blake and Bob Bryan.

Mardy Fish will team with Mike Bryan for Saturday's doubles against Feliciano Lopez and Fernando Verdasco.

Sunday's reverse singles will pit Nadal against former U.S. Open champion Roddick and Querrey against Ferrer. If the match is tied at 2-2, Querrey will face the added pressure of playing the final and deciding singles.

In the other semifinal, Argentina takes on Russia. No. 7 David Nalbandian of Argentina will play Igor Andreev in the opening singles in Buenos Aires, followed by Juan Martin del Potro against No. 6 Nikolay Davydenko. Argentina hasn't lost at home in 10 years.

Roddick, playing in his 17th straight Davis Cup series, said the 39th-ranked Querrey will benefit from playing the first match.

"It would be weird if Sam wasn't a little bit nervous going in," he said at Thursday's draw. "Maybe it's better for Sam not to sit around and think about it all day and get out there and hit some big serves."

The 6-foot-6 Querrey took a set off Nadal in a fourth-round loss at the U.S. Open this month and has a big serve that can trouble anyone.

But Nadal is coming off a career year, including his fourth straight French Open title, first Wimbledon championship and the Olympic gold medal in Beijing. He also took the No. 1 ranking from Roger Federer.

"I guess I'll make some faces at him, but I don't know how much that will do," Querrey said, when asked how he would try to psyche out Nadal. "I need to be aggressive and hit big serves and set the tone, do something. He's arguably the best clay-court player ever so it takes a lot to intimidate him."

Nadal is 2-0 against Querrey. He said the nearly four-month break since the close of the clay-court season means that even he was feeling a little rusty on this surface.

"He could have an advantage with his serve," Nadal said. "It's going to be, whatever the conditions, difficult."

A monthslong rift between the Spanish team and its federation was still simmering Friday. The players accused president Pedro Munoz of ignoring the team's suggestions and choosing Madrid as host to appease the Spanish capital, which is a Davis Cup sponsor.

"It's clear that if we were playing at sea level and if I would have been playing more recently on clay I would be more ready," Nadal said.

The Spanish team is worried that Madrid's high altitude will negate the advantage of clay courts, giving the big-serving Americans a boost.

"I hope so," U.S. team captain Patrick McEnroe said, when asked if the strife could help his team. "We're not counting on it though."

Ferrer has won two in a row over Roddick — on hard courts — to improve to 3-2 over the American.

"I'm going to be up against it that's for sure," Roddick said.

Mike Bryan will play in Davis Cup without brother Bob for the first time since the twins made their debut in 2003.

"What matters is that when the going gets tough, will they be as well connected as the brothers were?" Lopez said.

Spain hasn't lost on clay in more than nine years — a stretch of 15 series — and Nadal has lost only three of his last 124 matches on the surface. Nadal beat Roddick on clay in Seville to help Spain clinch the 2004 title.

"I'm sure it was a turning point in my career," said Nadal, who was a rookie for that final. "Beating Andy Roddick in the final was very important for my confidence."

Nadal (155) and Ferrer (130) each has way more singles wins on clay than the entire U.S. Davis Cup roster. The U.S. team has 86, including 67 by Roddick.

Still, Spain captain Emilio Sanchez Vicario said his players must be wary.

"If we think we'll win because we're favorites, we'll get 'caught out like the bull,' an expression that applies well to this series."

The U.S. is fielding a different lineup for the first time in 11 series.

"We're going to go out there and have fun," McEnroe said. "They have a lot of pressure on them playing at home. I think it's an opportunity for us to go out there and let our game fly."