Vaishali stretched her lead to 2.5 points following her second win under classical time control.

The Indian now has 8.5 points in her kitty and is followed by women's world champion Wenjun Ju of China and Anna Muzychuk of Ukraine.

Muzychuk defeated Koneru Humpy for her first win in the tournament while Wenjun got through her compatriot Tingjie Lei in the Armageddon.

With six rounds still remaining in the six-player double round-robin tournament, Lei stands fourth on five points, two points clear of Humpy and Cramling.

In the men's section, world number one Magnus Carlsen grinded down arch-rival Fabiano Caruana of United States on a day that witnessed all decisive games under classical time control.

In the other game of the day, Firouzja Alireza of France put it across reigning world champion Ding Liren of China.

The USD 1,61,000 prize money tournament has many more critical games to come but at the end of fourth round Nakamura has nosed ahead on seven points, enjoying a half point lead over Alireza.

Carlsen is third with six points to his credit while Praggnanandhaa slipped to fourth position on 5.5 points. Caruana is a close fifth at this stage with five points while Liren is a distant last on just 2.5 points thus far.

Vaishali won thanks to her perseverance out of a drawn rook and pawns endgame.

Playing the black side of a Grunfeld defense, the Chennai-based GM had little trouble equalising and the players arrived at a heavy piece endgame in almost no time.

Cramling had to solve her pawn structure problem a bit and this is where Vaishali thought she had a chance.

The game was still within the boundaries of a draw when Cramling blundered and found herself staring at a lost rook and pawns endgame. The game lasted 54 moves.

Humpy lost to Muzychuk in what was a similar story. The rook and pawns endgame should have been a draw but a blunder by Humpy towards the end sealed the fate of the game in Muzychuk's favour.

This was Muzychuk's first victory in Classical chess in almost seven months.

In the men's section, Nakamura capitalised on some unforced errors from Praggnanandhaa. The Nimzo Indian defense by the Indian resulted in a dynamic balance but Praggnanandhaa got too optimistic in the resulting middle game and sacrificed a knight.

The compensation, however, was not enough and Nakamura converted his extra material into a full point after 86 moves.

Carlsen defeated Caruana out of a Queen and pawns endgame. Outplaying his opponent from a balanced position has long been a hallmark of Carlsen and this day was no different as he won thanks to a blunder by Caruana in the final part of the game.

Results round 4:

Men: Hikaru Nakamura (USA, 7) beat R Praggnanandhaa (Ind, 5.5) 3-0; Fabiano Caruana (USA, 5) lost to Magnus Carlsen (Nor, 6) 0-3; Firouzja Alireza (Fra, 6.5) beat Ding Liren (Chn, 2.5) 3-0.

Women: Pia Cramling (Swe, 3) lost to R Vaishali (Ind, 8.5); Tingjie Lei (Chn, 5) lost to Wenjun Ju (Chn, 6); Anna Muzychuk (Ukr, 6) beat Koneru Humpy (Ind, 3).