James Hahn used a fast start and solid finish to edge one shot clear after Friday's second round of the Phoenix Open at the TPC Scottsdale.
Hahn fired a flawless 65 in ideal scoring conditions to post a 10-under total of 132.
Bidding for his second PGA Tour victory, Hahn birdied three of his first six holes and three of the last eight to end a sun-kissed day in the Arizona desert one ahead of American world No. 4 Rickie Fowler (68) and New Zealand's Danny Lee (66).
Hideki Matsuyama (70) and Irishman Shane Lowry (70), joint leaders with Fowler after the weather-delayed opening round, were a further two shots back in a three-way tie for fourth.