TURNBERRY, 1 Aug 2015, (AFP) - The 20-year-old shot a 69 in the horrendous conditions at Turnberry for an eight-under-par 208 total and she shared the lead with Taiwan's Teresa Lu, who also shot 69.
Suzann Pettersen, the halfway leader, had a 72 for third place on seven under with world number one Park Inbee poised for a final day attack on five under following a 69.
Ko opened with rounds of 68 and 71 and her 69 contained four birdies –- her only bogey was at the 16th -- but even she was surprised by her elevated position on the leaderboard.
"Today was a really good score and I never thought I would be leading such a big tournament," said the smiling youngster.
"I only had one practice round, but I have a really good caddie."
The man carrying her bag is Jeff Brighton from nearby Girvan. They only met on Tuesday.
"He's really nice and a very good player," said Ko. "He tells me that it is always like this in Scotland. The sun, rain, wind –- four seasons all in one day.
"I have never played in such terrible weather but it is very different and I'm enjoying it very much."
Lu's only win on the US-based LPGA Tour was in the 2013 Mizuno Classic in Japan but she also adapted well to the alien conditions.
The 27-year-old had five birdies in her 69 and she said her aim for the final day was to stay relaxed and enjoy it.
"Today I focused on playing low shots. It was fun," she remarked.
Six-time major winner Park Inbee is a big threat. The 27-year-old was another who carded a 69 and there is a hint that a great round is waiting to emerge from the great South Korean.
"We always expect this sort of weather in Scotland but I am really excited going into the final round," said the LPGA Champion. "Actually today we were quite lucky because the rain didn't last the whole way round."
Pettersen, two ahead overnight, started with a bogey and was out in 38. But the 33-year-old world number six birdied the tenth and 11th in a flawless back nine of 34 for a passable 72.
The best round of the day, however, was a 68 from Wales's Amy Boulden for three under par, while world number two Lydia Ko, joint second at halfway, could only manage a 72 and finished alongside Park on five under. But she is still a danger.
Leading third round scores Saturday at the Women’s British Open at Turnberry (par 72):
208 - Ko Jin-Young (KOR) 68 71 69, Teresa Lu (TPE) 68 71 69
209 - Suzann Pettersen (NOR) 68 69 72
210 - Mika Miyazato (JPN) 68 72 70
211 - Park Inbee (KOR) 69 73 69, Minjee Lee (AUS) 69 72 70, Lydia Ko (NZL) 66 73 72
212 - Melissa Reid (GBR) 73 70 69, Ryu So Yeon (KOR) 67 72 73
213 - Amy Boulden (GBR) 71 74 68, Nicole Broch Larsen (DEN) 69 74 70
214 – Maria McBride (SWE) 79 66 69, Anna Nordqvist (SWE) 69 72 73
215 - Julieta Granada (PAR) 70 74 71
216 – Lexi Thompson (USA) 71 75 70, Yani Tseng (TPE) 72 72 72, Alison Walshe (USA) 70 74 72, Cristie Kerr (USA) 66 77 73, Kim Hyo Joo (KOR) 65 78 73
217 - Candie Kung (TPE) 72 75 70, Hannah Burke (GBR) 74 72 71, Stacy Lewis (USA) 70 75 72
218 – Lunah Sobron (ESP) 70 77 71, Jane Park (USA) 72 74 72, Marianne Skarpnord (NOR) 71 74 73, Yoo Sun Young (KOR) 71 73 74, Christina Kim (USA) 71 72 75
219 - Chun In Gee (KOR) 72 76 71, Lee Jung Min (KOR) 70 75 74, Glwadys Nocera (FRA) 70 75 74, Florentyna Parker (GBR) 68 77 74, Amy Yang (KOR) 69 76 74