USA's Serena Williams in action against Russia's Anastasia Pavlyuchenkova at the 2016 Wimbledon Championships in London, Britain, July 5, 2016. [Photo/Agencies]

"But I have to say what I think really is my game is my mental toughness because just not only to be able to play, to win, but to be able to come back when I'm down.

"Both on the court and after tough losses, just to continue to come back and continue to fight, it's something that takes a lot of tenacity."

The world No.1 -- a position she has held for more than three years -- wrapped up the victory on her second match point with a 123 mph ace for 11 in total.