The American stormed through the first set in 27 minutes, not allowing her opponent to take any games. Martinez Sanchez found some confidence in the first half of the second set, stealing two games before falling to the 23 seed.
The match proved a stark contrast to her second round meeting with Kimiko Date-Krumm, which she clinched on an 8-6 tie-break in the third set.
“Thankfully I was able to get through a little easier,” she told the BBC. “The other match was three hours of non-stop running.”
Williams will next face Tvestana Pironkova, who ended second seed Vera Zvonareva’s competition this afternoon. The Russian was responsible for knocking Williams out last year.
“I’m looking forward to playing a little better last year,” she warned.