She holds the lead on 28 points – an outstanding tally helped by two eagles – at Siam Country Club’s Waterside Course, in the Asian Tour’s first ever Modified Stableford points event.
The US$750,000 tournament is also being jointly sanctioned with the Ladies European Tour.
The in-form 17-year-old from Chiang Mai, the winner of three domestic titles this year already, carded a six-under-par 66.
Thailand’s Natipong Srithong also made two eagles, including on the 18th, to move into second on 25 points with Korean Kyongjun Moon.
Reigning Asian Tour Order of Merit champion Joohyung Kim from Korea is fourth on 24 points and Indonesian Rory Hie is fifth with 23 points.
Rising Swedish star Maja Stark, who made a remarkable 17 points on the back nine thanks to an eagle and six birdies, is in sixth place with Thailand’s Jaravee Boonchant, on 22 points.
Overnight leader Sihwan Kim from the United States had a disappointing day after his opening 62 and shot 76 to finish on 20 points.
“Today, I played very well because I got two eagles and three birdies but on the ninth, my last hole, I got a bogey,” said Wannasaen, whose victories this year include two Trust Golf Mixed events.
“It is okay though because I got two eagles which was 10 points, so that was very good. My shots were perfect today.
“I didn’t change my gameplan, I just focused on myself and on my shots. I want to keep improving at every tournament that I play. For the final two rounds I am going to do the same and just focus on my shots and my routine.”
Natipong is looking for his first win on the Asian Tour since claiming the 2015 Resorts World Manila Masters and put himself in position to do that today after shooting a 63.
“I had a lot of chances for birdies and eagles. I was lucky to make two eagles on par fives. On number eight I hit my second shot near the green and chipped in, and on the last hole I hit driver and three iron onto the green and made a long putt,” he said.
“I’ve never played this format before and I was worried about counting the points, but I think it's good for my game and mentality to be aggressive and always go for the pin.”
Hie is showing the same kind of form which saw him lead after each of the first three days at the Gurugram Challenge last month on the Asian Development Tour. He eventually tied for fourth but had a very good excuse.
“I had Delhi belly, major headache and diarrhea on the last day,” said Hie.
“But I am kind of riding the momentum from the experience that I had there. Mentally I am more at peace with myself, taking it shot by shot, that seems to work pretty well for me. Staying in the present, deep breaths before each shot, just to make sure my mindset is in the right place. That’s my goal.”
Hie, who became the first player from his country to win on the Asian Tour when claimed the Classic Golf and Country Club International Championship in 2019 (which was played at the same venue as the Gurugram Challenge), said he is also enjoying playing the Stableford format.
He added: “I love this point system. I like it better than strokes because it gets you in a positive mindset, you are getting after the birdies; a birdie then a bogey is better than going par, par, it’s almost kind of like you are freewheeling it out there.”
Thailand’s star attraction Ratchanon “TK” Chantananuwat who claimed last week’s Trust Golf Asian Mixed Cup at the same venue missed the cut for the first time in eight starts on the Asian Tour.
“To be quite honest after I made that last putt on 18 on Sunday I felt really done, I am just tired. I tried my best, I wanted to be in the zone, I wanted world ranking points. No matter how hard I tried the putts would not go in. I just didn’t switch back into the zone I was in last week, or in every other week,” said the 15 year old.
“I got SEA Games next, I won’t let anyone down for that, I know what I need to do. I will practice as hard as I can for that one as what this week has shown me is that I have a curse upon me where if I don’t practice, I can never play good golf, and it seems to me it’s having more of an effect on me than anyone who plays golf.”
The golfing phenom confirmed he will compete in the International Series England and British Amateur in June.