Benoit Paire made a run to the Rome semis. Eidon Press/Zuma Press

The general consensus about this year's French Open is that the moment Roland Garros swings open its gates Sunday, Rafael Nadal and Serena Williams will begin a slow and inevitable procession to the men's and women's titles.

Barring an uprising from Novak Djokovic, this outcome is considered a fait accompli.

But take a moment, if you will, to ponder a more louche scenario: that this year's French Open could mark the return of a type of player who used to win this clay-court spectacular all the time, the type of player whose name is probably escaping you at the moment. We're talking about Andres Gomez, Michael Chang, Iva Majoli, Thomas Muster, Anastasia Myskina, Albert Costa, Francesca Schiavone and, in case you'd forgotten, the incomparable Gaston Gaudio.

Among the 256 players in the singles draws at Roland Garros, six are of special interest. WSJ's Carl Bialik reports on the favorites, the rivals and the upstarts.

Remember these tennis outsiders? They made the French Open their home for much of the Open era, which began in 1968. They are members of the not-so-exclusive club of men and women who have won this tournament in the Open era and never won any of the other Grand Slam events. The French also has the most one-time winners in the Open era of all the Grand Slam events.

Michael Chang won the 1989 French Open. Associated Press

Odds are this won't be the year the French Open returns to its little-guy roots. But there is a better chance than one might think. As superb as Nadal has been since returning from a seven-month injury layoff, his clay-court season hasn't been perfect and his knee remains a question mark. And for all her success on clay of late, Williams still hasn't won the French Open since 2002. Last year, she lost in the first round.

Nadal has lost just twice all season, won six titles and reached the final of all eight events he's played—impressive stats, to be sure. In April, though, Nadal lost in the Monte Carlo final for the first time in his career—in straight sets to Djokovic. In Madrid, he was two points from losing to David Ferrer, whom he had beaten, at that point, 14 straight times on clay. In Rome, he nearly lost a set at love against Ernests Gulbis.

Here's one thing that could work against Nadal at Roland Garros: rain.

In a conference call this week, John McEnroe said the courts at Roland Garros aren't watered as often as they used to be. "In my day they were watering the courts virtually after every set," he said. McEnroe didn't want to play on a damp court, he said, because it dulled his attacking game. But tennis is so different these days that a slow, muddy clay court works to Nadal's disadvantage, as last year's men's final showed.

There, as Nadal took on Djokovic in a light rain, his topspin forehand didn't bounce as high, allowing Djokovic to work him over—until play was postponed for the evening. Put Nadal on a wet clay court with Djokovic—or even Gulbis, Roger Federer, or Tomas Berdych—and he could suffer. Those men have enough firepower to hit through heavy conditions, just as Nadal is losing some of the spin that makes his shots so difficult to corral.

There are other intriguing outsiders among the men. Grigor Dimitrov, a 22-year-old long on talent but short on results, beat Djokovic in Madrid. There is also the 24-year-old Frenchman Benoit Paire, whose flashy game and theatrical court presence have recently produced results, including a straight-sets victory over Juan Martin del Potro in Rome (Paire eventually lost to Federer in the semifinals). A Frenchman hasn't won the French Open, or any other Grand Slam title, since Yannick Noah in Paris 30 years ago.

In recent years, the women have done a better job keeping to the traditional French script. Since Justine Henin won her last title in 2007, there have been five different French Open champions in five years.

Last year's winner, Maria Sharapova, was once so uncomfortable on clay that she described herself as a cow on ice. Sharapova had already won the other three majors, so she could hardly be classified as an outsider, no matter her distaste for clay. The same goes for Williams, who was favored to win in Paris last year when she arrived on a 17-match winning streak. Then, Williams lost in the first round, something she had never done at a Grand Slam event.

Williams takes a 24-match winning streak into Paris in search of her second title there. She won in both Madrid and Rome this month. But Williams has also hit a bump or two along the way, including a tight three-setter against Anabel Medina Garrigues in Madrid (Garrigues won the second set at love). "At some stage of the event, it would be likely that she won't have one of her best days," McEnroe said. "Someone might have a shot at her."

Williams lost just 14 total games in five matches in Rome, and trounced Victoria Azarenka, the world's No. 3 player, 6-1, 6-3 in the final. Still, she's wary of the outsiders in Paris. "Last year I was feeling excellent but didn't do great," she said. "This year I am cautious." At the French Open, that is the prudent choice.