Less than a month after Argentina's Angel Cabrera won the U.S. Open, players from that country were leading and tied for second in the national championship for golfers over age 50.
Romero shot a 6-under 66 over the Whistling Straits course.
Among those in the clubhouse at 69 were fellow-Argentine Vicente Fernandez as well as Jon Fiedler and Ron Vlosich.
Two-time defending champion Allen Doyle was 7-over through 13 holes.
Romero's round was highlighted by an eagle at the par-5 16th.
"Angel, he said to me, 'try to win the tournament, because two U.S. Opens in one month is fantastic,'" Romero said. "I say, 'Angel, I know it's hard, but I try my best.'"