The Japanese player had experienced an up-and-down day — two-over for the front nine, before birdies on three of her next four holes.
Korda had begun the day tied on nine-under 136 with fellow American Brianna Do, who was chasing her first LPGA tour title.
Korda enjoyed a calm, risk-free front nine, her eight pars punctuated only by a birdie on the par-five fifth.
She made a superb save with a long curling putt on nine to retain her solo lead over Arpichaya and China's Liu Yu.
But three-time major winner Korda turned the tempo down the stretch.
On the par-five 13th, her long eagle effort just failed to drop. She settled for a birdie, and a dart into the green on the par-three 14th meant a tap-in for another.
She struck a perfect driver followed by an aggressive iron on the low-scoring par-five 18th, to finish with a tap-in eagle.
Her only mistake of the day came when she twice tried and failed to retrieve the ball from the cup at the final green, laughing at her fumble.
Overnight co-leader Do had a more turbulent day. She had bogeys on the first and fourth, before pulling back birdies on six and nine to briefly move back into joint second.
But she sliced her tee shot into water on 10, carding a double bogey, and finished with a 72 on nine-under, tied for fourth with Liu.
Korda is having a totally dominant season.
She is already chasing her third win of 2026, having captured the Chevron Championship last week, and the season-opening Tournament of Champions
Korda finished second in her other three starts so far this year.