Best of Three: Djokovic emerges as Nadal's top French Open challenger

1. Meet the challenger: At this time of year, for the last half-decade or so, the burning tennis question has been: Can anyone beat Rafael Nadal at the French Open? Five times since 2005, the answer has, of course, been a resounding "no." Two top candidates, however, announced themselves last weekend. Novak Djokovic extended his 2011 winning streak by taking his hometown title, the Serbia Open in Belgrade. He beat Feliciano Lopez in the final. Djokovic now is up to 27 straight match wins this year and, especially with so many questions about his fitness answered in Key Biscayne, he must be considered Roland Garros contender 1B. We'll know more in the next few weeks.

2. The Big Four: Keep an eye on Juan Martin del Potro, the only player outside the Big Three to win a Major since 2005. After his injury-addled 2010, the Argentine is looking like a top five player again, riding his forehand to win after win. He took the title in Estoril on Sunday, demolishing Fernando Verdasco in the final. Del Potro is back in the top 50, with a bullet, and will likely wreak havoc on the draw in Paris. (Pity the poor seed who could potentially face him the first week!) And while he won't win the title, Nikolay Davydenko appears to be back in business as well. The industrious Russian, a nonentity since January, won the Munich title.

3. Lady Marmalade: For better or worse, the women's picture is looking as blurry as ever. Svetlana Kuznetsova, a former Roland Garros champ, was ousted from Madrid on Day 1. Ana Ivanovic, another former F.O. champ, appears to be back in slump mode, having just lost to Bethanie Mattek-Sands. (With all respect to Mattek-Sands, who has quietly -- loudly if we include her attire -- put together a fine career, Ivanovic HAS to find a way to win matches like this.) France's Aravene Rezai, a hot player a year ago this time, lost her first match to a qualifier as well.

Some winners from the weekend's smaller events -- and, thus, some de facto French Open dark horses: Italian veteran Roberta Vinci won in Barcelona for the fourth title of her career. (And we know that Italian veterans can succeed in Paris.) Another 28-year-old, Anabel Medina Garrigues of Spain, won in Estoril, her ninth career claycourt title and 10th overall.