Mel Evans, Associated Press
Exercise rider Michelle Nevin walks Big Brown around the stables at Pimlico Race Course.

BALTIMORE — Stuff does happen in thoroughbred racing's Triple Crown series. Big Brown is flying toward the June 7 Belmont Stakes as if on Pegasus wings, as uncatchable in Saturday's Preakness as he was in the May 3 Kentucky Derby.

But the tragedy of facts is that, more often than not — and not at all since 1978 — a Derby-Preakness double will not lead to the sport's most celebrated sweep. Since Affirmed last won all three, 10 champions at both Churchill Downs and Pimlico set themselves up as favorites to reign in New York, only to discover that you can't always get there from here.

"David would have never slayed Goliath if he had put his slingshot away," said trainer Kenny McPeek, who in 2002 saddled Sarava and watched that 70-1 shot knock off Derby-Preakness winner War Emblem. War Emblem fell to his knees leaving the gate and finished eighth.

"Horses stumble," McPeek said, "or the race doesn't get set up for him, or the rider makes an early move that was too soon, and the next thing you know, you've got a double-digit or triple-digit price on the board."

Spectacular Bid appeared poised to add to the string of Triple Crown winners in the 1970s — Secretariat in '73, Seattle Slew in '77, Affirmed in '78 — but finished third. Likewise, Pleasant Colony was third in 1981, Alysheba fourth in '87, Sunday Silence second in '89, Silver Charm second in '97, Real Quiet second in '98, Charismatic third in '99, Funny Cide third in 2003, Smarty Jones second in '04.

Even when a Triple Crown sweep hasn't been a possibility, Belmont favorites routinely have been upset; only twice in the last 12 years — and four times in 19 years — has the betting choice wound up in the winner's circle with Belmont's traditional carnation blanket.

Apart from the little things that can go wrong, as enumerated by McPeek, there is Belmont's challenging distance — 1 1/2 miles after the 1 1/4-mile Derby and 1-3/16-mile Preakness — coming as it does only five weeks after the first of the Triple Crown classics.

And, though the Preakness often has a drop-off in quality after the Derby — this year, horse people declared the field especially weak — it is not unusual for a rested, quality horse or two to be waiting at the Belmont. This time, the candidate for that role is the Japanese colt Casino Drive, who has raced (and won) only twice all year.

Which is not to say that Big Brown hasn't gotten race people all a-twitter. The consensus here, especially after Big Brown's extra-gear sprint off the final turn at the Preakness, is that the colt is a rare "monster," so dominant in his unbeaten five-race career that his jockey, Kent Desormeaux. used the same compliment — "freak" — for Big Brown that he applies to history's 11 Triple Crown winners.

"You've got to know what freaks they were, what resilience they had," Desormeaux said. "(With Big Brown), I know the gun's loaded. All I've got to do is pull the trigger."

Certainly, no one appears as convinced of his Triple Crown chances as Big Brown's hectoring trainer, Rick Dutrow, who all but promised victory before both the Kentucky Derby and Preakness.

When Desormeaux, who also rode Casino Drive in a May 10 Peter Pan victory, declared Casino Drive a worthy Belmont opponent for Big Brown, saying, "That's an exacta right there," he was asked, "Cold exacta (picking the winner and runner-up) or boxed (the first two horses in either order)?"

Before Desormeaux could answer, Dutrow put in, "Cold exacta."