Playing with black pieces, Das who has a rating of 2571 had a rook and two minor pieces against the latter's two rooks at the Khudiram Anushilan Kendra.
Bidita beat sixth seed Kundu in the only upset in the premier section with black in 13 moves in a Dutch defence.
IM Swayams Mishra (2539) sailed through with ease against young Utsav Mukherjee of Bengal as he obtained two rooks and extra pawns against his opponent's rook and knight.
About 700 players are vying for top honours in the seven round Swiss league Rapid Championship.
