Paris: Serena Williams was left furious following her bombshell second round exit from the French Open but vowed to work "five times harder" to repair her bruised status as the world's best player.

Serena Williams reacts during a break at Roland Garros yesterday. Pic/Getty Images
Serena Williams reacts during a break at Roland Garros yesterday. Pic/Getty Images 

To cap off a miserable day for the Williams' family, sister Venus was also knocked out as the two American superstars lost at a major on the same day for only the fourth time.

The top seed and 17-time Grand Slam winner lost 6-2, 6-2 to Spanish World No 35 Garbine Muguruza while Venus went out 2-6, 6-3, 6-4 to Slovak teenager Anna Schmiedlova.

"Obviously I'm super disappointed and, you know, it's hard. I worked really hard. But hey, maybe I can do better. I know for a fact I can work harder," said defending champion Serena. "I know for a fact I can play so much better than I did today, so it's a double-edged sword.

"If I couldn't play better I would be, I think, even more disappointed. But I know I can, so I know I have something to look forward to," added Williams who failed to reach the second week of a Grand Slam for the first time as top seed.

"I will have to work five times as hard to make sure it doesn't happen again," added the 32-year-old American who suffered her only Grand Slam first round loss in Paris in 2012. It was the earliest exit for a defending champion at Roland Garros since 2005 when Anastasia Myskina of Russia went out in Round 1.

Draw blown wide open
With the defeat the women's draw has been blown wide open as Williams joins second seed Li Na of China on the list of top casualties to crash out. It was the first time in the Open Era that the top two seeds had failed to get past Round 2 at a Grand Slam.