A cloudbust struck Monmouth Park 30 minutes before the $100,000 Invitation Handicap this afternoon, giving relief from the 95-degree heat and high humidity that had made viewing uncomfortable for most persons in the resort crowd of 22,274.

For the favorite-players the suffering wasn't over, however. They sent Silver Series of at 6 to 5 in search of his fifth straight victory in the Invitational, but it was Affiliate which struck light lightning along the rail at the head of the stretch to score by a length.

San Sebastian, a 25-toll shot, and Iron Constitution, the second choice, closed gamely through the final furlong of the 1 1/8 mile event to finish second and third, separated by a half-length Silver Series, perfectly placed by jockey Larry Snyder to move to the lead on the stretch turn, faded to fourth place, nearly three lengths out of the money.

Affiliate received an excellent ride from Miguel Rivera to return $8.80 straight for his first stakes success. The performance by the Puerto Rican jockey was reminiscent of his effort on Little Current in the 1974 Preakness Stakes Rivera saved ground all the way, then got through on the rail at the top of the stretch to steal off with the victory that afternoon. Today he did much the same thing with Affiliate.

Affiliate was fifth early, saving ground along the rail, and the chestnut colt by Unconscious never had to leave that favored position in making his move to the lead.

Tiny Monk and Prunneplum set the early pace, prompted by Silver Series, with Wilderness Bay fourth. Silver Series went to the outside under Snyder leaving the far turn and appeared ready to take command. But Rivera "cut the corner" with affiliate, charging inside Wilderness Bay, Pruneplum and Tiny Monk, then was upon Silver Series in a stride or two and challenging for the lead.

Affiliate put Silver Series away byfore reaching the eighth pole and had enough energy in reserve through the final sixteenth to hold safe late bids by Don Sebastian and Iron Consitution. The time was 1:50 3/5, after a mile in 1:37 1/5.

"The rail was the best part of the race track, before and after the storm," Rivera noted. "We wanted to stay there, if we were lucky enough. Everything broke just right once the leaders started getting a little tired."

Neither Affiliate nor Silver Series had run over a sloppy track previously.

"We didn't know how he'd do, although he'd worked well in the mud here," trainer Laz Barrera observed. "The heavy rains came so late, it was too late to put stickers on him, to help get a better footing. As it turned out, he couldn't have dun any better than the way he did."

The Travers Stakes at Saratoga on Aug. 20 will be Affiliate's next start. The chestnut colt owned by Habor View Farm had been second in the Hollywood Derby and Swaps Stakes (with Seattle fourth) in previous major appearances.

The Travers also was have been Silver Series' next outing, and probably still will be, although the gray colt had no excuse today except the lame comments offered by his jockey.

"He didn't take to the track as well as I would have liked," and the high weight certainly didn't help him in the off going," Snyder said.

Silver Series carried 126 pounds, attempting to spot his six rivals eight to 14 pounds. Trainer Oscar Dishman brought the Chieftain colt here nine days before the Invitational, giving the Midwest-baseed runner plenty of time to become acclaimated. Dishman did not, however, train Silver Series in the mud, avoiding that type of surface several mornings when the 3-year-old had been scheduled to work.

"My only worry is an off track," Dishman declared this morning. The racing surface couldn't have been sloppier, quickly turning into a rich brown meringue after the seventh race, which was decided on grass.

There were no late scatches from the Invitational, despite the weather. Nearly On Time was withdrawn from the feature this morning, in favor of the Whitney Stakes at Saratoga. The 3-year-old won the Whitney.