Ryu leads by three over Boeljon and by five over Italian Diana Luna and Ryu's fellow Korean, Ha Nuel Kim, with another shot back to the leading Australian Frances Bondad.
"Today my shots were not that great as my body condition is tired, said Ryu. "Yesterday I had a lot of energy but if I have a good sleep tonight then maybe tomorrow will be better. Yesterday I had a birdie chance on every hole but today I did not have many close birdie chances.
"My caddy told me to keep being patient and to think about my tempo and don't lose concentration."
When asked the shot that was the most memorable today Ryu was quick to answer. "Hole 17 the birdie putt. My tee shot at the par three 5th was also a good shot but at the 17th I concentrated on making it simple rather than worrying about technique.
"Every round I am trying to do that but today maybe my brain is so tired I couldn't concentrate on the ball as well."
"Tomorrow I will try hard to enjoy the tournament but I think I will need a lot of conversation with Tom (her caddy) because I want to relax my mind and just work on visualisation."
What would it mean to Ryu to win this event. "First I really like this course, this country and I would love to win this tournament as it really has a lot of tradition. A lot of players from a lot of countries have won this tournament and it would be nice to have my country's flag there (on the walk of champions)"
Of course Amy Yang was able to do just that in 2006 but Ryu may have been referring to having it there on more than one occasion as are the flags of Australia, England, Sweden and the USA.
There were occasions during today's round where it appeared as if the 21 year old Ryu might just be under threat. A bogey at the 2nd was followed immediately by three consecutive birdies, perhaps the highlight of that stretch being the 7 iron she hit to the par three 5th which finished a foot from the hole.
For several holes after that birdie blitz however Ryu appeared to be just treading water. She missed the fairway at the 9th and took bogey but the difference between her and her nearest chaser, Christel Boeljon of the Netherlands, was still four as she made the turn.
Boeljon, though, would close the gap to just two when she birdied the 11th and 12th holes and it was, for the moment at least, game on. Birdies at the 17th hole and 18th holes by the Korean however restored her command of the event.
While the margin is still a relatively large one, a number of other players staked their claim for a high finish and a possible win in the unlikely event of Ryu losing her way tomorrow.
Sydney's Frances Bondad won an event on the Ladies European Tour last October and the former Australian Stroke Play Champion appears to have been boosted by that performance after what has been a relatively quiet start to her professional career.
Today she took another giant step with a best round of the day, 63, to charge up the leaderboard. Bondad is a 24 year old from Sydney who underwent a course of Hypno Kinesiology last year after a specialist in that field felt the need to rid her of some of the subconscious demons which appeared to be holding her back.
Two weeks later she won in China and today is in contention for a significant domestic event. When Bondad finished more than two hours before the final group she was within five of the lead and, although that became seven by day's end and others had passed her, that she was able to produce such a low round speaks volumes for the progress she has made.
Any sceptics need only to look at what she is now achieving as a result of her sessions with Dr Adam Nichols of Sydney.
Also making significant moves were Italy's Diana Luna and the Korean, Ha Nuel Kim. Luna eagled the 15th and birdied the 17th and 18th to be home in 30 for a round of 66 and at 15 under is within five of the lead. But for a slow start on Thursday things could have been much better for Luna.
Also recovering from a slow start to the tournament was Kim who opened with an even par round of 72 on Thursday but then produced rounds of 65 and 64 to move into contention. Kim won three events on the Korean LPGA Tour last year and finished runner-up on two other occasions.
Kim also played the back nine in 30 the highlight of which was a 50 foot eagle putt at the final hole to at that point move within three of Ryu.
The field has a tough although not impossible task to catch Ryu tomorrow. If she gets the good night's sleep she is after she will take some serious catching but this is tournament golf and it can work in strange ways.
Ryu's caddy this week is Australian Tom Watson an experienced caddy who is on her bag for the first time this week as part of a four week trial to see how the combination works together. To say the least they have made a great start.
I thought I would ask Watson what his thoughts are of his new boss having worked for her for the first time this week.
"I think probably the most amazing things about her is that even though she is a 21 year old she is like a 40 year old veteran inside the ropes. It is like she has played the game for twenty years the way she thinks and the way she wants to play certain shots.
"Not many 21 year olds do that. At the same time when you get her outside the ropes she is like a 15 year old so she has a great capacity to switch on and switch off. They are the most impressive things about her."
It might just be that tomorrow Ryu will have fun both inside and outside the ropes.