Marksaeng birdied the first and last holes at the par-71 Phoenix Country Club, and had three birdies and a bogey in between to finish the third round at 8-under 205, two strokes ahead of second-round leader Tomohiro Kondo of Japan.
Kondo had a 70 Saturday and is two strokes ahead of American Brandt Snedeker (70), and compatriots Ryo Ishikawa (70) and Masaya Tomida (69).
Defending champion Ian Poulter of Britain shot a 66 for the days best score, and moved into a tie for 14th at 1-under 212.
The $2.1 million event is one of the richer tournaments on the Japanese mens tour. Recent winners include Tiger Woods (2004 and 05) and Padraig Harrington (2006).