HOYLAKE, United Kingdom, Sept 15, 2012 (AFP) - After all the wind problems that wiped out Friday's play, the 2008 winner at Sunningdale took advantage of the warm, calmer conditions to add a flawless 64 to her opening 71.
She led on nine under par 135 with another South Korean, and her playing partner, Park Inbee, the next best at four under following a 68.
With 36 holes to be played on Sunday, Japan's Mika Miyazato and Australia's three-time winner, Karrie Webb, start in joint third on three under. They both shot 70.
Shin, a former world No.1, missed a couple of months on Tour earlier in the year when she underwent a wrist operation, having had a piece of bone removed.
But she then claimed her first title in over two years by defeating American Paula Creamer in a nine-hole play-off last Monday at the Kingsmill Championship on the LPGA Tour.
She shot a nine under par 62 in the first round at Kingsmill, but she reckoned today's 64 that started with a chip in for eagle and three straight birdies was even better.
"I can't believe I just did that," was the 24-year-old's reaction after halves of 31 and 33. "My goal this week was to shoot one under par every round.
"But I made such a great start and I didn't have any bogeys and I didn't go in any bunkers so it was almost perfect."
"This Championship is so special to me. The win four years ago changed my life and I have lots of fans in England. I have so many good memories of playing over here.
"I also love links golf. It is such a great test and this is definitely my favourite week of the season."
World No.1 Yani Tseng is aiming to become the first three-in-a-row winner and, after two rounds of 72 for level par 144, tagging a win at Royal Liverpool onto Birkdale and Carnoustie is still not out of the question.
Lydia Ko, the 15-year-old New Zealand amateur, finished one shot better than Tseng after a 71. She goes into the final 36-holes tied for sixth and set to make even more of an impact on the world game.
As with Shin, Park also made her breakthrough in 2008 when she won the US Women's Open. Her second Tour title came in July at the Evian Masters in France, a tournament that will become the fifth major next year.
The 24-year-old is regarded as the best putter in the women's game and she showed her all round ability with three birdies and an eagle at the long 18th, her ninth hole.
The cut fell on five over par, and among those on the final mark was one of the joint first round leaders, South Korea's Kang Haeji.
She had an eight at the par four third hole but scraped in after she birdied two of her last three holes for a 79.
Ryu So-Yeon, who also opened with a 70, had an eight at the 18th (her ninth hole) but she recovered to shoot 74 for level par 144.
Leading second round scores on Saturday at the Women's British Open USLPGA and LET golf tournament (par 72):
135 - Shin Jiyai (KOR) 71-64
140 - Park Inbee (KOR) 72-68
141 - Mika Miyazato (JPN) 71-70, Karrie Webb (AUS) 71-70
142 - Katie Futcher (USA) 71-71
143 - Vicky Hurst (USA) 71-72, Lydia Ko (NZL) 72-71, Carin Koch (SWE) 72-71, Ai Miyazato (JPN) 71-72, Jenny Shin (KOR) 75-68
144 - Ryu So-Yeon (KOR) 70-74, Angela Stanford (USA) 72-72, Stacy Lewis (USA) 74-70, Yani Tseng (TPE) 72-72, Yuki Ichinose (JPN) 72-72, Katherine Hull (AUS) 72-72
145 - Cristie Kerr (USA) 72-73, Holly Clyburn (GBR) 72-73, Michelle Wie (USA) 75-70, Morgan Pressel (USA) 72-73, Paula Creamer (USA) 73-72, Amy Yang (KOR) 73-72, Julieta Granada (PAR) 74-71, Choi Chella (KOR) 72-73, Seo Hee-Kyung (KOR) 72-73