Kiradech Aphibarnrat fired a 66 to set the clubhouse target at the top of a congested leaderboard on day two of the Alfred Dunhill Links Championship.
The Thai held the lead on his own before a disappointing bogey on the last but a six under par round over the Old Course at St Andrews still got him to eight under in Scotland.
Overnight leader Paul Dunne, defending champion Tyrrell Hatton, Swede Joakim Lagergren and German Marcel Siem were all also eight under in the second half of their rounds.
The last of Aphibarnrat's three European Tour wins came in Scotland at the 2015 Saltire Energy Paul Lawrie Match Play but he has just three top tens so far this season.
He put that form to one side to birdie the first, fifth, sixth, eighth and ninth and when he rolled a beautiful putt across the tenth green, his lead was up to two. A 20-footer on the 15th got him to nine-under but he three-putted the last to drop into a group of five players.
Siem was also playing St Andrews and he made gains on the tenth, 18th, first, third and fourth in his first 14 holes.
Lagergren - who has finished fourth at this event in both his previous appearances - was also through 14 holes at Kingsbarns and recovered from an opening bogey with four birdies and an eagle.
Englishman Hatton made a hat-trick of birdies from the sixth at Carnoustie and after parring the 12th despite losing his ball off the tee, claimed another gain on the 13th.
Ireland's Dunne had to recover from an early bogey on the second at Carnoustie and made birdies on the third, sixth, tenth and 12th.
England's Ben Evans was then in the clubhouse at seven under after a 68 at Kingsbarns, with Scot David Drysdale on the same mark with one to play.
Former World Number One Luke Donald made five birdies in a row from the tenth at Carnoustie to sit at seven under with three to play, alongside Belgian Nicolas Colsaerts who had seven holes left at St Andrews.
English duo Tommy Fleetwood and Aaron Rai, German Bernd Ritthammer and Frenchman Romain Wattel were all at six under.