Playing with black pieces, Catherina exploited Mahalakshmi's weakness in the centre and gained a vital pawn in the twenty-fifth move. She maintained the pawn advantage till the end to seal the match in 66 moves.
Meanwhile, other overnight leaders Nimmy A G of Kerala and R Bharathi are at number two spot with seven and half points as they agreed to split the points after 45 moves in a Classical Sicilian game.
Seven players including top seed Chandika Divyasree, who beat Madhuri M Patil of Maharashtra are occupying the third spot with seven points.
In the eleventh and final round to be held tomorrow morning, Catheina takes on Nimmy with white pieces, while Bhrathi is pitted against state mate P Priya with dark colour pieces.