March 9 (Reuters) - Argentine Fabian Gomez and American Scott Brown share the lead at 18-under at the Puerto Rico Open as they head into Sunday's final round four strokes clear of the field. Gomez, searching for a maiden PGA Tour victory, shot a seven-under round of 65 at the Trump International Golf Club with his one bogey coming on the 10th hole. Brown, from Augusta, Georgia, had a five-under 67, also with just one bogey.