Top seed Serena Williams looked a little shaky in her 7-6 (5), 6-3 win over Kiki Bertens in the second round of the US Open. But she then showed why she's the world number one.
Williams' serve was a particular problem during her victory, with the American serving ten double faults and landing just 59 percent of her first serves.
So, following her match, and it's important to mention that the heat at Flushing Meadows is so intense that players are collapsing on court, Williams immediately went back out onto the practice courts and practiced serving for 90 minutes – because you don't win 21 grand slams by being satisfied by a below-par performance.
— Pam Shriver (@PHShriver) September 2, 2015
You almost have to feel for her third round opponent, Bethanie Mattek-Sands, because we think the Williams serve will be back with vengeance.