After winning the 2015 Wimbledon championship, Serena Williams is just one step away from doing what no women’s tennis player has done in 27 years. Just the U.S. Open stands between the sport’s best player and all four Grand Slam championships in a calendar year.

Considering only three women have ever accomplished the feat, it won’t be easy for Williams to win the 2015 U.S. Open in September. But Williams has been so dominant that it would be an upset if she doesn’t make history.