PARIS - No one went quite so far as to blame a Day 1 loss at the French Open on - or credit a victory to - the different tennis balls being used this year at the clay-court Grand Slam tournament.

There were, though, plenty of opinions about the switch of spheres.

They're harder, most agreed. They're fluffier, a few thought. They're better, some suggested, for players such as Rafael Nadal, who use a lot of spin. They're faster, at least at first, then tend to slow after a few games. They'll help powerful servers.

Any of those elements could affect matches, players said, and possibly their health.

"In the locker room, a lot of the girls ... (are) coming in with a lot of shoulder issues. They say the balls are pretty hard," the highest-ranked American woman entered in the tournament, Bethanie Mattek-Sands, said Sunday after coming back to beat Arantxa Parra Santonja of Spain 2-6, 7-6 (5), 6-3.

"I think it kind of translates to they're going fast through the air," said Mattek-Sands, who was 36th in the most recent rankings, trailing Serena and Venus Williams, who withdrew from the French Open. "I don't mind that. I actually like it if it's fast-paced."

Under a five-year contract that begins in 2011, the French Open is moving to Babolat balls from Dunlop. It's not every day that a Grand Slam tournament changes its ball brand. Or even every century. Wimbledon, for example, has used Slazenger since 1902. The U.S. Open has used Wilson since the late 1970s. The Australian Open switched to Wilson in 2006.

Pro tennis players can be rather persnickety about the equipment they use, noticing any slight tweak as they move from tournament to tournament. The European clay circuit events leading up to the French Open in recent weeks used Dunlop balls.

"The balls are pretty strange," 14th-seeded Stanislas Wawrinka of Switzerland said after winning Sunday. "Obviously I do notice a big difference from last year."

The 2010 women's runner-up, Sam Stosur of Australia, wasn't so sure.

"They might be a little bit harder," said Stosur, who defeated Iveta Benesova of the Czech Republic 6-2, 6-3 in the first match on Court Philippe Chatrier. "I don't think that's a bad thing or a good thing. It's just what they are."