Gary A. Tanaka's pacesetting Riddlesdown forgot to stop in Sunday's $100,000 Mac Diarmida Handicap (gr. IIIT) at Gulfstream and jockey Roger Velez guided him to a 1 1/2-length upset at 29-1. The final time for the 1 3/8-mile turf test was 2:14.75. On the bit early, the 6-year-old Irish-bred son of Common Grounds established command through fractions of :25.31 for the quarter-mile and :49.80 for the half as pace rivals Marquette, Just Listen and Rochester conceded the early lead. Velez slowed it down on the backstretch while maintaining a two-to- three-length advantage in a six-furlong split of 1:14.98 and 1:39.07 for the mile. On the final turn, Rochester, a 3-1 co-favorite in the full field of 12, offered a mild bid but soon faded as Riddlesdown kicked for home and another Irish-bred, Macaw, took up the chase. Macaw finished second, two lengths ahead of Just Listen, who edged Williams News by a head for the show spot.Co-favored Whitmore's Conn was not a factor.Niall O'Callaghan trains the chestnut Riddlesdown, who won for the second time in his last three tries (awarded first by disqualification in the Oct. 25 John Henry at Arlington Park). It was Riddlesdown's third win in nine starts since coming to the U.S. for Tanaka more than a year ago. Overall, he sports an 8-3-1 record in 26 starts with earnings of $264,954.Riddlesdown, who carried 113 pounds to his first graded stakes win, paid $61.60, $32 and $22.40. Macaw, ridden by Jose Santos, returned $10.80 and $8.60. Just Listen, With Rosemary B. Homeister in the irons, paid $21.80. The all-Irish exacta was $607.80 and the boxcar trifecta was worth $10,515.