The great American champion was shocked by little-known Harmony Tan, a 24-year-old Frenchwoman ranked 113th in the world.

Tan was making her Wimbledon main-draw debut. Williams has been coming to Wimbledon since 1998, when her opponent was still a babe in arms, reaching 11 finals and winning seven of them.

But you would never have known this from the contest as Tan rose to the occasion, beating Williams 7-5 1-6 7-6 (10-7).

Tan, on the verge of tears, said :"I don't know what to say. I have watched so many times on TV. For my first Wimbledon it is 'wow', just 'wow'."

"When I saw the draw I was really scared - Serena, she's a legend. I was like, 'oh my God! How can I play? I can win maybe one or two games."

The loss leaves Williams still one major short of matching Australian Court's record 24 grand slam titles and, turning 41 in September, running out of opportunities.

Having not played a singles match since being forced to retire with a torn hamstring in the first round last year, and only two doubles matches with Ons Jabeur at Eastbourne last week, Williams was inevitably rusty.

It was no surprise when she lost the first two games to Tan, but nor was it when she won the next four.

Then the plot twisted. Tan broke back and held to be 4-4, then broke again at 5-5 before serving out to claim the set.

Tan had game point on Williams' serve at the start of the second set, but the seven-times champion held.

That enabled the veteran to put the pressure back on Tan. Her first service game of the second set lasted 19 seconds shy of 20 minutes, and at the end of it Williams had broken for a 2-0 lead.

She grabbed the momentum that established and ran with it all the way to take the stanza 6-1.

Surely now she would romp to victory? It looked like it as, to the delight of an adoring centre-court crowd, she raced into a 3-1 lead in the decider. But Tan was resilient. Breaking back she went into a 4-3 lead.

But Williams broke again to be 5-4 ahead, and serving.

Tan came back, breaking again, then holding to force Williams to serve to stay in the championships.

It went to 30-30, then a wayward volley handed Tan match point. To roars of delight Williams saved it before taking the match into a tiebreak as the match clock ticked beyond three hours.

Williams raced into a 4-0 lead, but Tan simply would go away fighting back to lead 5-4.

Williams fought back and the tie ebbed and flowed before suddenly Tan had another match point. This time, with a rasping forehand, she took it.

Australian Associated Press