She really exposed Peng's defensive limitations. She has no footspeed and no reach with the two handed grip on both wings. Her only defense consisted of mid-court dying swans moonballs. Not a good matchup for Peng given Petra's lefty placement and strong power. No way Petra should ever lose to this limited player.
It's a win, but is the game displayed enough to beat Serena? Unless she motivates herself better in this potential match-up, I don't see it. Also, let's not forget it was an indoors match, something Petra should be particularly good at.