Stephens has struggled for form since reaching her first ever Grand Slam semi-final at the Australian Open in January, and her injury-prone Chinese counter-part made it two wins from two against the young American.
"It was cold out there but I had a good start, probably because I played so much yesterday," said Peng, who played twice on Wednesday at the rain-hit clay court event.
Alize Cornet beat Chanelle Scheepers 6-3 6-1 to reach the semi-finals of the Strasbourg International.
Runner-up last year, Cornet was on the cusp of victory against the South African when rain halted the play with Cornet 5-1 in the second, but, when play resumed, she fired a backhand pass to clinch the victory.
She will be joined there by Canadian teenager Eugenie Bouchard who beat Anna Tatishvili of Georgia 6-3 6-2 – the youngster breaking her opponent twice in each set to move into the semi-final of a tournament for the first time.
WTA Strasbourg results
3-Alize Cornet (France) beat 7-Chanelle Scheepers (South Africa) 6-3 6-1
Eugenie Bouchard (Canada) beat Anna Tatishvili (Georgia) 6-3 6-2
Romina Oprandi (Switzerland) beat Zheng Jie (China) 6-3 3-6 6-0
8-Peng Shuai (China) beat 4-Sloane Stephens (U.S.) 6-2 6-3
2-Roberta Vinci (Italy) beat Yulia Putintseva (Kazakhstan) 6-3 5-7 6-2
Jamie Hampton (U.S.) beat 5-Kirsten Flipkens (Belgium) 6-4 3-6 7-5