Serena Williams [ Images ] suffered her first defeat of the year on Sunday when she was beaten 6-3, 6-4 by Justine Henin-Hardenne in the final of the Family Circle Cup.

The world number one, who completed her 'Serena Slam' in January when she won the Australian Open [ Images ] to hold all four Grand Slams at the same time, surrendered a 21-match winning streak with defeat at the $1.3 million tournament.

"Today was an off day and you can't be on your off day against a top player," Williams told reporters.
 
"She (Henin-Hardenne) played really excellent today. She had a good plan going out there and it all worked.
 
"She was on today and she was really fighting. She did a great job."

Having suffered her previous loss at the season-ending WTA Tour Championships last November -- to Henin's fellow Belgian Kim Clijsters [ Images ] -- the American had entered the final as the overwhelming favourite against a player she had beaten four times in five meetings.

But a determined Henin-Hardenne came out fighting on Sunday to upset the formbook and tame a rather subdued Williams.
 
The top seed's usual armoury of winners seemed to have deserted her as she erratically sprayed her shots wide and surrendered the match on her serve with a weak backhand into the net.

Williams had been hoping to win her fourth consecutive event of the year but instead had to see a jubilant Henin-Hardenne throw her arms up in the air to celebrate her second victory of the season.

"It's still very tough to beat Serena and today I just kept fighting and finally won the match," said the 20-year-old Belgian, who also triumphed in Dubai [ Images ] in February.

"She's number one in the world and she deserves that so much. But I agree that for me on the clay court it's much easier than on the other surfaces because we could see that I had much more time to organise my game.

"I just tried to stay focused and just believe in my chances and believe I can do it, play point after point, and then I just went all over the court."