Romero and Vaughan shot a 3-under 68, giving them a one-shot edge over Andy Bean, John Cook, Kirk Hanefield and Nick Job. Watson was in a six-way tie for seventh at 71. Included in that group was Bernhard Langer.
Norman led into the final round at Royal Birkdale last Sunday and a win would have made him the oldest major champion in golf history. But the 53-year-old Norman finished six shots behind champion Padraig Harrington and he began this tournament with a 75.
"This golf tournament is like any other, you just need to hang in," Norman said. "There's more than one round to a golf tournament."
Watson won five British Open titles and he has captured three of the last five Senior British Opens.
"I didn't hit every fairway, but I hit every green today," Watson said. "I don't think I've ever hit 18 greens on the tour ever in my life."