Serena Williams charged to her sixth Wimbledon title on Saturday. The 33-year-old American beat Spain's Garbine Muguruza 6-4 6-4 to win the first three legs of the 2015 Grand Slam. If she wins the U.S. Open in September, she will hold all four 2015 Grand Slam titles, becoming the first woman to achieve that since Steffi Graf in 1988 "I'm just happy it was such a great match. I can 't believe I'm standing here with another "Serena Slam There was definitely a bit of pressure towards the end," Williams explained after the match.