Goryachkina had been considered a tough challenge for the Vietnamese master with a superior Elo rating of 2,466. The 18-year-old player, who is seen as a child prodigy of Russian chess, won the world youth crown twice in 2013 and 2014.
Meanwhile, Nguyen was nearly 100 places behind Goryachkina with an Elo rating of 2,351.
However, the Elo gap did not matter for the Russian competitor as she failed to make a better fist against an exceptional Thao Nguyen in the second round.
Nguyen managed to hold Goryachkina to a tie in the first game before finishing victorious within 69 moves in the second game, which lasted nearly five hours.
Earlier, in the first round, the Vietnamese representative also performed brilliantly, beating a much more highly rated player, Georgian Lela Javakhishvili (Elo 2,455) with the same score of 1.5-0.5 (one draw and one win).
Next up for Nguyen will be a third-round crunch encounter against world No. 3 Anna Muzychuk (Elo 2,558), who is also reigning world rapid and blitz chess champion.
The tournament is taking place from February 10 to March 5 with the presence of 64 players, including many world-famous names such as former world champion Alexandra Kosteniuk (Russia), Zhu Chen (Qatar), Antoaneta Stefanova (Bulgaria) and Ju Wenju (China).
A total of US$450,000 is up for grabs, with each receiving US$3,750 for the first round, US$5,500 for the second round and US$8,000 for the third round. The overall winner will be awarded US$60,000 in prize money.
