That victory took her into the semi-finals, making her the first US teenager to reach the last four of a grand slam since Serena at the 2001 US Open.
Stephens became an instant celebrity. She had 17,000 followers on Twitter before her match point against Serena and 35,000 an hour later. But with fame comes pressure and the American has struggled to cope with it since, or live up to expectations.
Stephens, 20, has failed to win back-to-back matches at any tournament since the Australian Open, winning only two of her eight duels and getting a walkover past an injured Venus Williams in Miami.
The constant attention has put the world No 16 off her game. Back in February, after her first-round loss to Sorana Cirstea at the Dubai Tennis Championships, Stephens was asked if she was enjoying being the centre of attention.
"No, not really," she said. "I wish you guys would all just forget about me and just let me do whatever. That's obviously not going to happen. I'm definitely working with you guys and hanging in there."
Stephens will have to do better than just "hanging in there" if she hopes to fulfil her potential.
She will have to learn to live with all this attention and, here, she could learn a few things from her idol, Serena.