On the eve of the Blue Grass Stakes, Wayne Lukas said Marfa had developed into a top racehorse because he had become more mature, more professional. "It used to be that 25 percent of the time he'd do what I wanted, and 75 percent what he wanted," the trainer said. "Now, it's about 50-50."

Marfa was doing just what Lukas wanted today when he swooped outside the leaders on the turn at Keeneland and looked ready to draw away to a decisive victory. But instead of going on to establish himself as the solid favorite for the Kentucky Derby, he started behaving like the greenest of horses, like the old Marfa. He refused to run in a straight line, prevented jockey Jorge Velasquez from riding him, practically knocked down two of his rivals and lost by a neck to Play Fellow, a 19-to-1 shot.

If he had won that photo finish, it wouldn't have mattered. Marfa was disqualified and placed fourth for interfering with Desert Wine and Copelan, although those colts weren't going to be close to the winner at the finish. Neither was the Maryland entrant, Deputed Testamony, who finished sixth.

Although excuses will be offered for plenty of horses in the Blue Grass field, because of the trouble in the stretch and the sloppy condition of the track, only Marfa and Play Fellow emerge with credentials as legitimate Derby contenders. And they are strong contenders, indeed. Their time, 1:49 2/5 for the 1 1/8 miles, was excellent, and they have the stretch-running style that succeeds at Churchill Downs.

The Blue Grass unfolded as expected, as Desert Wine and Copelan--each of whom had once been considered the country's leading 3-year-old--battled for the early lead. They set a respectable pace, although hardly a suicidal one, racing the first half-mile in :46 2/5 and the three-quarters in 1:11, while the highly regarded Highland Park stalked them.

Approaching the turn, Marfa and Play Fellow made their moves simultaneously and started gaining on the leaders with every stride. Even though jockey Jean Cruguet was saving ground on the rail, Marfa was outmoving him as he swooped outside Copelan and Desert Wine. Then the fun began.

While Play Fellow was cutting the corner and getting through on the rail, Marfa tried to lug in, forcing Velasquez to yank him away from Desert Wine. But after a few more strides, he did swerve into Desert Wine. "I got sawed off pretty good," jockey Chris McCarron said. "I had to pull my colt up completely."

Marfa continued lugging in toward Copelan, who had Play Fellow just inside him. "It was like two slices of bread coming together and I was the ham," jockey Jerry Bailey said. He had to stand up in the irons to avoid a disaster. Then Marfa moved toward Play Fellow until they were flank to flank. Play Fellow outdueled him to the wire, but if Marfa had kept a straight course, he surely would have won.

Desert Wine finished the race 7 1/2 lengths behind the leaders in third place, with Copelan another length behind in fourth place, but they were moved up to second and third after the Marfa disqualification.

This was a victory that Play Fellow--who paid $40.80, $13 and $6.40--needed badly. He had shown signs of ability in Florida this winter, closingly strongly to be third in the Everglades Stakes before running badly in the Flamingo Stakes when his jockey lost the irons.

But he had earned only $44,864 before today, and seemed unlikely to get into the Derby because of the rule limiting the field to the 20 starters with the greatest career earnings. Now he is heading straight for Louisville. So is Marfa--although it may be wrong to assume that he can go straight anywhere.