A new opening — Marshall Attack — helped city-based grandmaster Diptayan Ghosh to checkmate former World Championship challenger Ian Nepomniachtchi of Russia in Round II of the Chess World Cup at Resort Rio in North Goa on Wednesday.

Tuesday’s match, where Diptayan played with White pieces, had ended in a draw.

Diptayan, a former winner of The Telegraph Schools’ Chess, have never used that opening and tried it against Nepo, as the Russian is called by his peers, on senior pro and grandmaster Surya Sekhar Ganguly’s advice. It paid rich dividends.

This was the biggest upset of the tournament till now and also a major achievement in Diptayan’s playing career. For Nepo, who got a first-round bye, it was a case of “came, saw and lost”.

“Before the tournament, I had some sessions with Aranyak (Ghosh) and Surya. It was Surya’s advice to try out the Marshall Attack.

“The opening caught Nepo by surprise. And in the middle game, he made a blunder, probably because of that,” Diptayan, seeded 117th, told The Telegraph. Nepo was the 12th seed.

Diptayan came to Goa with his parents, Sandip and Aruna. They were travelling with him for the first time in 12-13 years.

“India is hosting the World Cup after more than two decades. That’s why he insisted that we accompany him to Goa. “We witnessed the biggest win of his life. Our presence also helps him to relax after the matches,” father Sandip said.

Diptayan, 27, next plays the winner of the match between Armenian Gabriel Sargissian and Israel’s Maxim Rodshtein on Friday.

“Will watch the tie-breaker tomorrow (Thursday),” Diptayan, a former banker, said.

Reigning world champion and tournament top seed Dommaraju Gukesh, India No 1 Arjun Erigaisi and Pentala Harikrishna also advanced to the third round.