The German Sophia Popov survived both the conditions and a bout of nerves to claim the Women's Open at Royal Troon.
The world number 304 admitted she nearly walked away from the sport last year and had previously never won on the LPGA Tour or Ladies European Tour.
A final round of 68 was enough to finish on seven under par, two shots ahead of Thailand's Jasmine Suwannapura. Minjee Lee and Inbee Park were the only other players in the field to finish below par.
Popov had only earned £82,500 in her career previously but banked the top prize of £515,500 for the victory as well as a first Major title. "I got here on Tuesday and I knew my game was in really good shape," she said.
"I took that belief into every round but I didn't expect this. I was uber nervous the whole round. I was glad I could get it done."