RIO GRANDE, 7 Mar 2015 (AFP) - Brown, whose only tour crown came at this event two years ago, fired a bogey-free five-under par 67 to join Smith, who shot 68, on six-under 210.
Argentina's Emiliano Grillo and American Jon Curran were one stroke off the pace while Canada's Adam Hadwin, Zimbabwe's Brendon de Jonge, Paraguay's Fabrizio Zanotti, American Scott Pinckney and 36-hole leader Alex Cejka of Germany were another shot adrift.
De Jonge, at 87th in the world, is the highest-ranked player in the event, being played opposite a World Golf Championships event at Doral that has lured the world's top players.
Brown birdied the par-5 second and fifth holes and closed the front nine with a birdie, then finished birdie-birdie to claim his share of the lead.
Smith, in his 319th PGA event at age 45, won his only crown at the 2002 Buick Classic, the last time he led entering the final round. He has not cracked the top 10 in a PGA event in nearly a decade, since 2005 in Milwaukee.
Argentina Open winner Grillo, 22, is playing on a sponsor's exemption and if he wins following a triumph last week at the Honda Classic by Irishman Padraig Harrington on a sponsor's exemption, it will mark the first time such entrants have won in back-to-back weeks in PGA history.
Leading scores after Saturday's third round of the $3 million US PGA Tour Puerto Rico Open (USA unless noted, par-72)
210 - Scott Brown 73-70-67, Chris Smith 69-73-68
211 - Jon Curran 70-71-70, Emiliano Grillo (ARG) 69-70-72
212 - Adam Hadwin (CAN) 72-72-68, Fabrizio Zanotti (PAR) 72-71-69, Scott Pinckney 70-71-71, Brendon de Jonge (ZIM) 71-70-71, Alex Cejka (GER) 70-67-75
213 - Johnson Wagner 75-71-67, Rafael Cabrera Bello (ESP) 70-75-68, Boo Weekley 74-71-68, Martin Flores 72-73-68, Sam Saunders 72-72-69, Michael Bradley 71-72-70, Mark Hubbard 68-74-71, Chad Collins 70-72-71, Gonzalo Fernandez-Castano (ESP) 73-69-71, Jonathan Byrd 70-71-72
214 - YE Yang (KOR) 74-72-68, Tim Petrovic 75-71-68, Andres Romero (ARG) 72-73-69, Will MacKenzie 75-69-70, Dicky Pride 70-74-70, Greg Owen (ENG) 74-70-70, John Daly 72-70-72, Rod Pampling (AUS) 70-71-73