Serena Williams has admitted that she does not know what went wrong in Saturday's shock defeat to Alize Cornet at Wimbledon.
The world number one was left stunned as Cornet recovered from a first-set loss to beat the five-time champion and consign her to a third-round exit - her earliest elimination since 2005.
"Right now I don't really know what I did wrong," she told reporters.
"Usually I do. Usually I know I did this, that or that. I have a few ideas, but this will be a really good one for me to assess and figure out what I can do, to do better next time.
"That's happened to me a few times, but it's fun: it kind of gives you a mission to work on, gives you goals to work towards to see what you can do better."
Cornet faces Eugenie Bouchard in the next round.
