Garbine Muguruza and Serena Williams pose with their trophies.  [Photo/Agencies]

Williams dug deep to get back to 3-2 sparking a scream of defiance from a player who had been in 26 Grand Slam finals dating back to 1999 and lost just five of them.

But Muguruza was solid on her serve despite the occasional double fault and the Spaniard went 4-2 and then 5-3 up.

Williams saved four match points in the next game to stay alive, but Muguruza stayed calm to serve out for the biggest win of her fledgling career, clinching it with a lob that landed smack on the baseline.