RIO GRANDE, Puerto Rico, March 7, 2013 (AFP) - Percy, seeking his first US PGA title, made nine birdies against two bogeys at the Trump International resort while Romero, whose only PGA crown came in 2008 at New Orleans, fired seven birdies and an eagle against a pair of bogeys.
Americans Jon Curran and Blayne Barber shared third on 66 while a group of nine players on 67 included Argentina's Angel Cabrera, Canada's Brad Fritsch, Puerto Rico's Rafael Campos and former US Amateur champion Peter Uihlein.
With 65 of the tour's top players at the World Golf Championships event at Doral in Miami this week, the Puerto Rico event offers a title chance to some of the PGA's unheralded standouts.
Romero began on the back nine and had back-to-back birdies at the 12th and 13th holes, then added birdies at the par-3 16th and par-5 18th ahead of his eagle at the par-5 second.
The 31-year-old South American followed that with birdies on three of the next four holes before stumbling back with bogeys at the par-4 seventh and par-3 eighth holes.
Percy, whose best US PGA showing was a runner-up finish at Las Vegas in 2010, opened with back-to-back birdies before a bogey at the fourth, then answered with birdies on three of the next four holes.
After beginning the back nine with a bogey, Percy answered with birdies at the 12th and 13th holes, another at the 16th and closed with a birdie as well.
Leading finishers on Thursday after the first round of the $3.5 million US PGA Puerto Rico Open (USA unless noted, par 72)
65 - Anders Romero (ARG), Cameron Percy (AUS)
66 - Blayne Barber, Jon Curran
67 - Angel Cabrera (ARG), Bill Lunde, Steve LeBrun, Brad Fritsch (CAN), Justin Bolli, Morgan Hoffman, Brian Stuard, Peter Uihlein, Rafael Campos (PUR)
68 - Robert Karlsson (SWE), Colt Knost, Dicky Pride, James Driscoll, David Hearn (CAN), Heath Slocum, Bryce Molder, Scott Brown, Luke List, Matt Bettencourt, Josh Teater, Henrik Stenson (SWE), Chris Stroud, Brendon Todd
WD - Kim Si-woo (KOR)