Cameron Young fired a round of 70 to move six shots clear at the Cadillac Championship at Trump National in Doral.
Starting the day with a bogey at the par-five first, Young recovered to make four birdies though he did make bogey on 13.
How moves on 15 under, with Scottie Scheffler, SW Kim and Kristoffer Reitan sharing second spot on nine under.
A shot further back are Ben Griffin, Matt MacCarty and Nick Taylor.
After a disappointing 75 on Friday, Shane Lowry improved with a 70 on Saturday, in a round where he recovered from dropped shots on three and six to make five birdies. However, he dropped another shot on 17 and lies at one over.
Jordan Spieth took a significant dive, shooting 75 and falling to a tie for 12th at five under. He was hurt by two double-bogeys - first on the par-three fourth when he didn't get into putting position until his fourth stroke and then on the 18th when his approach shot went into the water and he was forced to take a penalty.
Meanwhile United States captain Jim Furyk has named Justin Leonard and Stewart Cink as vice captains for the 2027 Ryder Cup.
Furyk was last month named as the man to try and regain the trophy after Tiger Woods passed on the opportunity to lead the US at Adare Manor.
And the 55-year-old, who has been involved in every Ryder Cup since 1997, has begun assembling his backroom team for Limerick with the appointments of Leonard and Cink.
Leonard famously sank a lengthy putt to secure the Ryder Cup for the US at Brookline in 1999 while Cink featured in five successive Ryder Cups between 2002 and 2010.
Europe won the 2025 edition with a historic victory at Bethpage Black, maintaining a strong recent record in the competition.
Furyk will try to become the first US captain to win on European soil since Tom Watson led his country to a 15-13 win at the Belfry in 1993.
