Serena chasing tennis history at the French Open

Challengers to Serena Williams' throne have proved as fickle as a Paris spring and as the year's second grand slam starts the veteran American is again seemingly in a league of her own.

The 34-year-old's charge to overhaul Margaret Court's record 24 grand slam singles titles may have stalled since she chalked up major number 21 at last year's Wimbledon.

But after fine-tuning her claycourt game by winning last week's Italian Open she will begin the defence of her French Open title as the strong favourite.

With twice French Open champion Maria Sharapova suspended pending the findings of an anti-doping hearing after she tested positive for Meldonium in Australia this year, the list of players capable of toppling a fully firing Williams is short.

She has played only three tournaments since losing to an inspired Angelique Kerber in the Australian Open final. But former champion Martina Navratilova says when the big prizes are at stake, the American can be relied upon to perform.

"She hasn't played that much this year, but she came back with a vengeance (in Rome), played great tennis, as well as she has on clay, and she is the big favourite going into the French Open," 18-times grand slam champion Navratilova told the Tennis Podcast in the build-up to Paris.

"When she loses it's an exception... Serena is now healthy, hungry, eager and fresh. She's match-tough after Rome, but still fresh - that's a tough combination, and it will be hard for anyone to beat her."

The main obstacles between Williams and a 22nd singles major which would take her level with Steffi Graff in second place, appear to be Germany's Kerber and former world number one Victoria Azarenka, although both have struggled for consistency.

Kerber suffered first-round defeats in Rome and Madrid, although she did win the title on clay in Stuttgart.

Azarenka, ranked five, was back to her best when winning back-to-back titles at Indian Wells and Miami, but doubts have resurfaced.

She suffered a back injury in Madrid and lost in the first round in Rome.

"It's just unfortunate that I can't play my best tennis. That's it," Azarenka said after losing to Irina Begu in Rome.

Others contenders will be Romanian former finalists Simona Halep and Spain's hard-hitting Garbine Muguruza.

Muguruza, a semi-finalist in Rome, does not have the trademark claycourt game, relying on flat, powerful groundstrokes that could however cause damage at Roland Garros, where the showcourts tend to play fast.

Three-times champion Williams though, as is usually the case, appears to have the destiny of the tournament on her racket strings.

"I have tried to defend there once, twice... before. Didn't quite work so well. But this year is different," she said. "I feel more calm and I don't feel stress, like I have to win. I feel like just happy to be out here."