Dissatisfied Serena hits practice court immediately after 2nd-round win

Even as she played far from her best, Serena Williams did enough to win her second-round US Open match against Kiki Bertens on Wednesday.

But Serena Williams isn't Serena Williams because she's satisfied with "enough."

"You know, I don't think you should be happy with just winning," Williams said after the match. "At least I'm not. Maybe other people can. ... You know, if I don't play well, I'm not going to be happy even if I won."

Williams was nervy and inconsistent throughout the match, and struggled tremendously with her serve, double-faulting 10 times and winning just 33 percent of points on the second serves she managed to land.

So, before even hitting her post-match press conference, she snuck in a few minutes on the practice court to get some serves in, under the watchful eye of coach Patrick Mouratoglou.

"Patrick told me some things that he saw that he thought I could work on to improve it and to get better," Serena said when asked about her impromptu practice session.

"We'll see. I'll see tomorrow how I am in practice, how I am with serving. I'll see how I do tomorrow."