The first question about Genuine Risk is: Where did she sneak onto the course?

Rosie Ruiz "wins" the Boston Marathon, presumably by taking a taxi to within sight of the finish line. And now comes a girl horse, a filly, the first one to run in the Kentucky Derby in 21 years -- and she wins the thing, the first filly to win in 65 years. So even as we speak, a dozen shamefaced colts are reviewing films to see how she did it. They hope to spot her leaving the track to catch the subway to the quarter pole.

Sorry, guys.

The lady just kicked your hindquarters.

She was in full sight all the way around the mile and a quarter at Churchill Downs, in full sight of the 131,859 customers here and millions more on national television. For those male chauvinists who passed her off as a frivolous dame playing in a man's game -- sort of a Janet Guthrie with four feet -- Genuine Risk gave them all the evidence they needed with about three-eighths of a mile to go.

She looked lost. There she was, running in a four-horse bunch right behind the three leaders. Up ahead were Plugged Nickle and Rockhill Native, the favorites, and Bold 'N Rulling. Genuine Risk was third from the rail in the second gang of runners when, suddenly, she stopped.

Not to be sexist about this, because, heaven knows, men who drive cars sometimes are hesitant. But the way Genuine Risk suddenly slowed down right there where many a Derby is won or lost, even Janet Guthrie would have said, "Hey, she's forgot which one is the brake and which one is the gas."

Genuine Risk dropped out of the second pack. Then, as suddenly as she looked beaten, the filly looked sensational. She knew what she was doing all the time. At least, her jockery, Jacinto Vasquez, knew. He was looking for room to run and first he had to slow down, then guide his lady around all these slowpoke guys clogging up the expressway.

"I was right between some horses," said Vasquez, who rode Foolish Pleasure to win the 1975 Derby, "and I had a lot of pressure from the inside. I had a horse outside me, too. And I know some horse is going to come from behind and I'm going to be stuck.

"That's why I took back and went to the outside. I waited to see what the front horses were going to do. If they go out. I want to drop in. If they stay in, I'm going to stay outside."

They stayed in. The lady stayed out. With a long run around the far turn, going around six horses, passing the first group in a lane maybe 20 feet off the rail. Genuine Risk proved beyond question she was the best of this lot on this day. No shortcuts necessary.

This was a surprise, of course. It was a surprise she was even in the race. Only two weeks ago when she finished third in the Wood Memorial, her trainer, LeRoy Jolley, said Genuine Risk would not run in the Derby. That the Wood was her first defeat in seven career races was only one factor in Jolley's decision; history was most of it.

History says fillies shouldn't run against good colts. The good colts are too strong. There's a lot of money a filly can make running against other girls. So why bother with the guys?

Nature comes in here, too. It is yet spring in the Bluegrass, and in the spring a young filly's heart soars on the wings of desire. She doesn't want to run away from colts, she wants to see their etchings. "Fillies in the fall" is the way the horsemen say it, meaning they save the girls for those cool days when ardor slumbers.

And perhaps memory played a part. One of sport's saddest days involved the great filly Ruffian, a grand-looking runner with a champion's hear and ability. They arrange a match race in 1975 at Aqueduct, sending the champion Ruffian against the champion Foolish Pleasure.

Jolley trained Foolish Pleasure.

A quarter of a mile into the match race, Ruffian, straining to keep head and head with the colt, shattered a front leg. She hobbled in pain, the leg dangling grotesquely, blood streaming over the hoof.

"We threw a fast quarter as her . . . and she unbuckled," said Jolley's father, the famous trainer Moody Jolley.

LeRoy Jolley was kinder. He said the filly killed herself trying. And maybe that is why he would have prefered keeping Genuine Risk away from the big, strong colts.

In any case, she came to Churchill Downs. The owners, Bert and Diana Firestone, said no decision to stay away was made after the Wood.

"Nothing ventured, nothing gained," he said.

"It's always been in our schedule," she said. "It suited her pedigree, it suited her schedule."

Bert Firestone said the only equivocation was over the size of the Derby field. After the Wood, in which the winning Plugged Nickle bumped Genuine Risk coming down the stretch, Firestone was worried that a 20-horse Derby could get his nice filly bumped again.

"We didn't want to risk getting her hurt," he said. "On the Sunday and Monday after the Wood, we talked again with LeRoy and said we'd think it over. We'd go down and watch the Blue Grass (five days after the Wood, 10 days before the Derby) and see how the competition is shaping up.

"After the Blue Grass, there were only 12 or 13 in the race. So we changed our minds."

It is open to debate how much of a change in mind there is when you already have shipped a horse from New York to Kentucky before the Blue Grass -- as the Firestones did with Genuine Risk. That isn't done for exercise. But it's a quibbler's point, incidental to the larger story of how a filly wins the race that makes colts rich and famous forever.

The quick answer is: the colts this year are bums. So what if a filly beat them? Tamara Press could whip Truman Capote's hindquarters at wristwrestling. Someone asked Jacinto Vasquez if his filly could win the Belmont at 1 1/2 miles, and the jockey said, "With this competition, she can go two miles."

A better answer starts with the filly's breeding. It is wonderful. Her sire is Exclusive Native, whose offspring include Affirmed and 51 other stakes winners. Three Derby winners are her relatives on a sire line that goes through Raise A Native and Native Dancer.

It wasn't all that mysterious, then, that the Firestones gave their 13-year-old son $35,000 with which to buy the tilly. When you own a 1,400-acre farm near Waterford, Va., and have bought the Aga Khan's place in Ireland, your 13-year-old son can be given $35,000 worth of credit. So at a yearling sale two summers ago, Mathew Fireston began bidding.

He brought in the filly at $32,000. Today he said he did it because she was "a very good-looking horse. She's put together right."

So here we have a $32,000 filly bought by a 13-year-old rich kid who was in a military school at the time.

What you do next, if you have a good-looking runner, is hire LeRoy Jolley to teach her how to run so fast she won't need a taxi. In seven Derby starts now, Jolley has produced two winners, two runners-up and a third-place finisher. "LeRoy is probably the best trainer in American," Bert Firestone said. "He deserves all the credit for us winning the Derby."

Then you hire a rider who has had success with fillies -- Vasquez rode Ruffian, was on her that last cruel day -- and you leave it up to him to find a way around the studs that drew most of the $10,122,067 bet today. Of that total, $296,214 was bet on the filly -- $132,913 of it on her nose. One presumes most of that money came out of ladies' purses, just as the $28.60 return will go to buy lots of Chanel No. 5.

Since Silver Spoon finished fifth in 1959 -- 44 years after Regret won -- no girl had tried the Derby until now. There had been 275 colts in the 20 races since '59. Of tose 20 winners, only 12 went the mile and a quarter faster than the filly's time of 2:02 today.

Women runners can smile again.