Romero, the Argentine player who won the PGA Tour’s 2008 New Orleans event and the European Tour’s 2007 Deutsche Bank tournament, had an eagle and seven birdies on his first 15 holes to reach 9-under, then fell back with the bogeys on the par-4 seventh and par-5 eighth.
Percy, from Australia, had nine birdies and two bogeys on the Trump International course.
Blayne Barber and Jon Curran were a stroke back, and two-time major champion Angel Cabrera opened with 67 to match Bill Lunde, Steve LeBrun, Brad Fritsch, Justin Bolli, Morgan Hoffmann, Brian Stuard, Peter Uihlein and Rafael Campos. Patrick Cantlay, the 20-year-old former UCLA player coming off a Web.com Tour victory last week in Colombia, shot 70.
Romero has missed the cuts in four of his five starts this year, shooting 75-67 last week in the Honda Open.
Percy, a five-time winner on the Australasian Tour, tied for 71st in the Honda Classic, wasting a 71-66 start with weekend rounds of 77 and 78.
WEB.COM TOUR: In Santiago, Chile, Whee Kim had an eagle, seven birdies and one bogey en route to an opening-round 8-under-par 64, taking a one-shot lead in the Chile Classic.
Augusta’s Scott Parel shot 68 and trails by four while Aiken natives Kevin Kisner and Matt Hendrix shot 71s and Aiken resident Stephen Poole opened with 72.