Qatar's two times Dakar winner Nasser al-Attiyah slipped to third overall in his Toyota, an hour and 12 minutes behind Sainz.
"It was a really long day again and we tried to push. We did not make any mistakes, but we are a little bit tired this evening," said Peterhansel.
"Today it was a really important stage...not easy, and I think tomorrow in Fiambala it will be the same."
Sainz was still smarting from a 10 minute penalty applied on Monday for an alleged collision with Dutch quadbike rider Kees Koolen.
Peugeot have said they intend to appeal the sanction.
The day's bigger drama came in the motorcycle category, with Frenchman Adrien van Beveren crashing out and handing the overall lead to Austrian Matthias Walkner.
The Yamaha rider was evacuated by helicopter after a high-speed fall three kilometres from the finish of the 373km special stage between Salta and Belen. Organisers said he had broken his right collarbone and injured his thorax and spine.
Walkner won the stage and took over at the top, leading Spaniard Joan Barreda by 39 minutes.
Wednesday's 11th stage runs from Belen to Fiambala and Chilecito.
(Reporting by Alan Baldwin, editing by Toby Davis)
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