The South Korean opened her account with a round of 72 before adding a 73 on Friday, a sequence which saw her seven shots off the pace set by Inbee Park heading into the weekend's running.
However, Ryu found her feet on Saturday, with a fantastic round of 65 moving her to within one shot of Park. The 24-year-old built on her 65 with a closing round of 69 to finish a shot clear of Park who was only able to register a 71 on Sunday.
“I didn’t expect that I had a chance to win this tournament, because in the second and first rounds, I didn’t play really well,” Ryu said of her turnaround.
“Fortunately I was able to shoot eight under in the third round so after that I was in contention.
“I’m really proud of myself, because it’s good to be back in contention and our group was exciting, with Inbee and Suzann [Pettersen]. It was good to play with Inbee, my best friend on the tour. She is not number one right now, but I believe she is the true number one, so it was great to compete with her.”
Park, who had at least a share of the lead over the first three rounds, was gracious in defeat.
“It was a consistent day today but my putts wouldn’t drop into the hole," said the world number two.
"It was really just the putting that was the only problem and So Yeon played well. Even with the double bogey, she played really well and I’m really happy for her. If I didn’t win, I kind of hoped that she would win, so it’s kind of good that my best friend won the tournament and I’m ready to congratulate her.”