HYDERABAD, DEC 9: Top seed K Sasikiran produced a six-move mating combination to cash in on a blunder committed by IM Arun Vaidya and BT Muralikrishnan shocked twelfth seed Verghese Koshy in the fifth round games of the 2nd Global Trust Bank Fide-rated chess tournament at Oxford Plaza, here, on Tuesday.Playing Modern Defence, Koshy made things difficult for himself taking a pawn at c5 on move 15. Murali sacrificed two more minor pieces in exchange for the queen and then harrassed the black king no end to finally mate it at b8 on move 28.Muralikrishnan thus remained in the lead along with D V Prasad, P Mithrakanth and Rahul Shetty. All four have five points each.Prasad scored a gutsy win over Anup Deshmukh, perhaps indicating that he is at last regaining the form that had deserted him in the recent tournaments.Mithrakanth cowed down giant-killer Visweswaran, while Rahul Shetty pulled the rug from under the feet of second seed P.Konguvel.Sai Meera, overnight joint leader, failed to extend her winning sequence as she settled for a draw against Roktim Badhopadhyay.