On a day when Parimarjan Negi played out a draw with Radoslav Wojtaszek of Poland, Krishnan Sasikiran scored his first victory at the expense of out-of-sort Abhijeet Gupta.
With just four rounds remaining in the category-18 six-player double round robin tournament, Korobov remains in front with four points out of a possible six and Alekseev remained on his toes half a point behind.
Negi and top seed Wojtaszek share the third spot on three points apiece, while Sasikiran, 2.5 points, edged himself ahead of Gupta (2) after an easy victory.
Korobov played the white side of a Nimzo Indian hoping for an advantage in one of the main lines. However, Alekseev was well armed to tackle the intricacies of the sharp middle game and the Ukrainian thought it better to go for equalising variations.
Korobov went for heaps of exchanges to reach a level endgame that was drawn vide repetition of moves.
Negi faced the Sicilian Najdorf by Wojtaszek and an opening Novelty by the Indian gave some advantage after Wojtaszek decided to sacrifice an exchange early.
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The position got simplified in quick time and Wojtaszek had two pawns and a minor piece for a lost rook which offered enough counter play for the Polish.
Negi stood optically better but the position was probably not headed anywhere. A draw was a just result.