LOUISVILLE, Ky. - Giacomo, a horse named after the son of rock musician Sting, stung 19 rivals and bettors who played the obvious contenders in Saturday’s Kentucky Derby, posting a 50-1 upset that was the second-largest shock in the 131-year history of the race.

The California-based colt rallied from well back in the pack to grab the lead in the final strides, winning by a half length over Closing Argument, himself a 71-1 long shot. Afleet Alex, the 4-1 second choice in the race, finished another half length back in third. Running time was 2:02.75, well off the record set by Secretariat in 1973.

Giacomo, ridden to victory by veteran jockey Mike Smith and trained by Derby newcomer John Shirreffs, returned $102.60 to faithful fans willing to overlook the fact that he had only one previous victory on his résumé. The victory also triggered a series of astronomical “exotic” payoffs for bets involving multiple horses, topped by a $1 superfecta payoff of $864,253.50.

The second largest crowd in Derby history — 156,435 — watched the thrilling upset.

Giacomo’s dramatic charge also disarmed trainer Nick Zito’s record-tying arsenal of five Derby starters for five different owners. The best finish by Zito’s highly regarded quintet was a fading seventh by George Steinbrenner’s 5-2 favorite, Bellamy Road.

“I was waiting for one of my horses and they never came,” Zito said after watching his bid for a third Derby victory come up dry.

FREE VIDEO Surprise at the Derby May 7: See 50-1 longshot Giacomo win the 131st Kentucky Derby.

The result probably won’t lift the Boss’s spirits, even though the Yankees ended a four-game losing streak with a 5-0 win over the Oakland Athletics on Saturday.

Giacomo, a son of Holy Bull owned by executive Jerry Moss of A&M Records and his wife, Ann, was the beneficiary of the second-fastest pace for the first three-quarters of a mile in Derby history.

As Spanish Chestnut was setting sizzling fractions of :22.28; :45.38 and 1:09.59, pursued closely by Going Wild and Bellamy’s Road, Giacomo was relaxed in 18^th position and wide, about a dozen lengths behind the leader.

The testing pace began to take its toll as the leaders reached the top of the stretch. Bellamy Road stuck his head in front, only to face an immediate challenge as stablemate High Fly, Closing Argument and Afleet Alex rallied into contention.

Giacomo was still 11^th, but only about five lengths behind the leaders and closing fast with a quarter mile to run.

Smith’s Derby experience – he had three second-place finishes from 11 previous mounts – paid dividends for Team Giacomo as the jockey threaded his mount through the moving maze of fading horses.

Derby longshots Highest payoffs for winners of the Kentucky Derby since $2 mutuel bets began in 1911 with winner, year and price: ?Donerail, 1913, $184.90 ?Giacomo, 2005, $102.60 ?Gallahadian, 1940, $72.40 ?Charismatic, 1999, $64.60 ?Proud Clarion, 1967, $62.20 ?Exterminator, 1918, $61.20 ?Dark Star, 1953, $51.80 ?Thunder Gulch, 1995, $51.00 ?Gato Del Sol, 1982, $44.40 ?Bold Venture, 1936, $43.00 ?War Emblem, 2002, $43.00

The 39-year-old journeyman found a seam entering the stretch and guided Giacomo to the outside at the quarter pole, where he had a clear shot at Closing Argument, who had gotten to the front and was slowly getting the best of Afleet Alex.

Giacomo responded to Smith’s furious left-handed whipping to overhaul Closing Argument and was slowly drawing away at the wire.

“I’m so numb, I can’t even tell you how I feel,” Smith said at the post-race news conference. “When I stood up at the wire, it was like all the strength just left my body.”

Smith and Moss both heaped praise on the soft-spoken Shirreffs, a 59-year-old Vietnam veteran who has been training since in California since 1978 but was saddling his first Derby starter.