Petrova lost her serve four times in the match but managed to break Peng seven times to clinch the victory.
The 25-year-old Peng had won both her previous matches against Petrova this year in three sets.
Ana Ivanovic was to meet Roberta Vinci later Thursday on the opening day of the eight-player tournament. It features the six highest-ranked players who have won a title during the season but did not qualify for the WTA Championships and two wild cards.
It is the final event on the WTA calendar.