Here's a little history that shows why John McEnroe was right to say Serena Williams would lose to a low-ranked male professional, and why Serena Williams so readily admitted it in 2013.

In 1998, a smoking, beer-drinking German, 15 years older than Serena and her sister, Venus, beat both sisters like rented mules. And that was after a suds-soaked round of golf. Wikipedia has the details:

See Braasch’s own report here: How to... beat both Williams sisters in one afternoon, by Karsten Braasch, Observer, September 2, 2001.

Now, why is it we so desperately want women in combat?