Romero, who was tied for the lead after the first round, shot his second consecutive 65.
Romero birdied six of the last 10 holes on the Trump International course.
Brown holed out from 170 yards for eagle on the par-4 seventh and had eight birdies and a bogey.
Brown played the Web.com Tour the past two weeks, finishing third in Panama and tying for seventh in Colombia. He tied for 30th at Pebble Beach in his only other PGA Tour start.
“I’ve played really good all year,” Brown said. “I haven’t been making a lot of putts, but I’ve been hitting it really good and a lot of the putts haven’t been going in, I think good putts. So I knew it was coming.”
WEB.COM TOUR: In Santiago, Chile, Edward Loar shot his second consecutive 65 and has a two-shot lead at the Chile Classic at Prince of Wales Country Club.
Aiken’s Kevin Kisner shot 67 and is tied for 35th.
Scott Parel, Matt Hendrix and Stephen Poole all missed the cut.