Romero, the Argentine star who won the 2006 JELD-WEN Tradition for his lone title on the 50-and-over tour, had a 12-under 132 total on the Sonoma Golf Club course.
Watson shot 64, and Thorpe, the 2003 and 2006 winner, had 69. Thorpe earned the last spot in the field, edging Tom Jenkins by $4,079 for 30th place on the money list.
Brad Bryant shot 67 to join Tom Purtzer (67) and Joe Ozaki (65) at 9 under. Mark James (70) was 8 under.
Jay Haas, 165 points behind leader Loren Roberts in the Charles Schwab Cup standings, was 6 under after 70. Tom Watson, seeking his fourth victory in the season-ending tournament, was 1 over after a 71.
GINN SUR MER CLASSIC: In Port St. Lucie, Fla., Daniel Chopra fired his second consecutive bogey-free round, 7-under-par 66, to get to 13 under and within one shot of leaders Bob Estes and Tommy Armour III in the suspended second round of the rain-soaked PGA Tour event.
Estes and Armour shot 68s after identical 64s on Thursday.
Chopra played the first two rounds with Estes and Bob Tway, who started his opening round with four consecutive birdies - and that seemed to set the tone for a two-day scoring barrage by the group. Combined, they have 39 birdies and six bogeys entering the weekend. Tway had shot 70-70 and is eight shots off the lead.
Aiken native Matt Hendrix, who opened with 73, is 1 under through nine holes.
HONDA LPGA: In Pattaya, Thailand, Suzann Pettersen shot 4-under-par 68 for a two-shot lead in the LPGA Tour event.
Pettersen holed a 115-yard wedge shot for eagle on the par-4 13th and birdied the 18th. She's at 11-under 133, two shots clear of Canadian Alena Sharp (68).
MALLORCA CLASSIC: In Son Servera, Robert-Jan Derksen and Jean-Francois Lucquin shot 5-under-par 65s to share the lead in the European Tour event, with 54 players left on the course when the second round was suspended by darkness.
Derksen and Lucquin were at 9-under 131, three shots ahead of Peter Lawrie (68) and Mads Vibe-Hastrup (66) on the Pula Golf Club course.
MICCOSUKEE CHAMPIONSHIP: In Miami, rain halted second-round play before anyone could finish their round in the Nationwide Tour event.
Marc Turnesa is the leader on the course. Turnesa, who opened with 4-under-par 67, is 4 under through nine holes and 8 under for the tournament. He leads first-round leader Dustin Bray, who is 1 under through six holes and 7 under for the tournament.
Former Thomson resident Franklin Langham, and Augusta's Scott Parel, did not tee off. Langham opened with 68 and Parel had 69.