Sania and Martina, top seeds here, took just 90 minutes to get past the challenge of fourth-seeded Timea Babos of Hungary and Kristina Mladenovic of France 6-4 7-5 in their final round-robin match and finish on top of their group.
By virtue of this win, Sania and Martina had avenged their loss to the same pair the last time they played in Rome this year.
The Indo-Swiss pair got break point opportunities at 4-all in the first set and 5-all in the second, and grabbed the chances with both hands to serve both sets out.
"We had played them twice before and we were 1-all, so we knew we had to come out and play well, like we've been trying to do every match here at the WTA Finals," Sania said after the match.
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"We just tried to come out and play our best, and that was enough to win today."
Sania and Martina are just two wins away from their ninth WTA doubles title since joining forces eight months ago.
"It feels pretty good!" Martina said after the victory.
"Sania came up to me and asked me why don't we try to play together, and at first we both had our partners, but as soon as we started we won a hat-trick right away at Indian Wells, Miami and Charleston. It was amazing how fast we clicked.
Sania and Martina will face third seeds, Chan Hao-Ching and Chan Yung-Jan of Chinese Taipei in the semifinals.
Sania had won the women's doubles title at last year's WTA Finals with Cara Black of Zimbabwe.