Only in Hollywood could they have dreamed up such a spectacular finish to thoroughbred racing's biggest day. Wild Again, an implausible 31-1 shot, won a photo finish from Gate Dancer and Slew o' Gold to finish first in the $3 million Breeders' Cup Classic.

Then he survived a controversial stewards' inquiry into a bumping incident during the stretch that led to Gate Dancer's disqualification from second place. The crowd of 64,254 booed the verdict lustily. The stunning upset climaxed a day that had already produced high drama and brilliant performances. Royal Heroine equaled a world record in winning the one-mile turf race. Fran's Valentine suffered the most expensive disqualification in history in the $1 million race for 2-year-old fillies. Princess Rooney gave the best performance of the day, winning the 1 1/4-mile Breeders' Cup Distaff a full second faster than Wild Again ran.

But of the seven championship events that were run before a national television audience on this first Breeders' Cup day, it was the Classic that will be most remembered -- and debated.

Slew o' Gold came into the race with an unbeaten 1984 record but with a troublesome right front hoof. Gate Dancer was supposed to be his major foe. The only attention paid to Wild Again came from incredulity that his owners, the Black Chip Stable, had paid $360,000 to make him eligible for a race in which he appeared to have no chance.

And for most of the Classic, Wild Again looked as if he had no chance. He engaged in a suicidal battle for the lead, sandwiched between swift Precisionist and Slew o' Gold's "rabbit," Mugatea. While they went a half mile in an enervating :45 3/5, Slew o' Gold remained in perfect position in the middle of the pack, and Gate Dancer was trailing. Wild Again disposed of his early competition, but Slew o' Gold drew abreast of him, and Gate Dancer started to accelerate on the outside.

In midstretch, it became clear that Slew o' Gold wasn't going to get past the tiring leader. "He just didn't seem willing to run," said Wild Again's jockey, Pat Day. But Gate Dancer was accelerating strongly, and for a moment, jockey Laffit Pincay Jr. said, "I thought I was going to win easy."

But then the colt in the purple earmuffs started to display the bad habits that had plagued him through the Triple Crown series. He was lugging in toward the two leaders, and even powerful Pincay couldn't control him. Slew o' Gold was in tight quarters between his two rivals, and Gate Dancer kept making things tighter. Then Wild Again seemed to drift slightly in Slew o' Gold's direction, squeezing the 3-5 favorite out of contention.

When the photo finish disclosed that Wild Again had won by a head, having covered the 1 1/4 miles in a slow 2:03 2/5, the INQUIRY sign was lighted and no one could have envied the stewards this tough decision. Even Day couldn't claim that he was completely innocent. "My horse wanted to get out all the way," he conceded. But the stewards concluded that Wild Again had maintained a generally straight course, and that Gate Dancer had done most of the damage.

"Gate Dancer lugged in the last sixteenth of a mile," said steward Pete Peterson, "and placed Slew o' Gold in close quarters. Actually he interfered with both inside horses."

Wild Again paid $64.60, $10.80 and $3.60. Slew o' Gold returned $3 and $2.20 and Gate Dancer paid $2.60 to show. Those payoffs were relatively unimportant to the Hollywood Park fans who bet more than $700,000 on the Pick Six, encompassing the last six Breeders' Cup races. When Wild Again's number stayed on the board, nobody picked all six.

Wild Again had scored some big-money victories before today, but he had never defeated competition of this quality before. He had lost a minor prep race as a 1-2 favorite; he had a poor workout; he lost his scheduled jockey when Eddie Maple took the mount on Track Barron instead. But the people around him never lost faith. "I've always thought he was one of the best horses in the country," trainer Vincent Timphony said. "I never considered him any 30-1 shot. That's why we put up the $360,000."

Because Slew o' Gold was sub-par physically and Gate Dancer wouldn't run straight, Wild Again made racing history. Because of the way the Breeders' Cup alters all the arithmetic of the game, he now ranks as one of the top-money winning thoroughbreds of all time, with earnings of more than $2 million.

Other landmarks were set in this race. Gate Dancer and Slew o' Gold lost the most expensive photo finish in the history of the sport. Eddie Maple made history, too. "I believe," he said, "that this is the first time my agent has taken me off the winner of a $3 million race."