India, April 9 -- Two years ago, Praggnanandhaa and Vaishali strode into history as the first brother-sister pair to ever play the Candidates tournament. This time, one of them is coming to terms with a missed chance, while the other is in contention for first place.

In the all-Indian clash in Round 9, Vaishali outplayed Divya Deshmukh with the white pieces, moving up to 5.5 points and into a co-lead with Zhu Jiner. It brought up Vaishali's third win in four games. Going into Wednesday's games, five players, including Divya, were in shared first place. Now, that group has been trimmed to just two players.

Vaishali, who chose the Reti opening (1.Nf3) and transposed to the English opening, steadily moved into an advantage on the board and...