Off Topic - a nice riddle

A friend of mine put a nice riddle in his blog (there's more if you are interested)

Here it is:

The question is how many matches do you need to hold in a grand slam, to declare the winner, when the number of starting players is 8192?

To answer this question you don't need to use any advanced math and not even a calculator. The less math you use and the more logic you apply - the easier and faster the answer gets...

(Just to make it clear, in a grand slam tournament, if you lose - you are out, the winner continues to the next game).

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