Brandon Wu edged into a one-stroke lead after shooting a five-under 67 in the Puerto Rico Open second round on Friday.
The American backed up his opening-round 66 with another fine showing to get to 11 under at the halfway mark of the PGA Tour event in Rio Grande.
Wu was one under through 11 holes in his second round before picking up four shots on his final seven.
He sits a shot ahead of Greg Chalmers, the Australian carding a 68 as he chases his first PGA Tour success since 2016.
Branden Grace (68) and Rafael Campos (69) are tied for third at nine under, a stroke clear of Jhonattan Vegas (68), Cameron Percy (69), Nelson Ledesma (67) and Thomas Pieters (67).