St. Brendan won the $50,000-added Riggs Handicap at Pimlico today, but the most excitement came when Dr. Peatoppy, a superior claiming horse who had been racing as an obscure claimer named Sun Dandy, won the ninth race at odds of 7 to 1.

Then, as an added twist to the already bizarre circumstances surrounding the switched horses, Dr. Peatoppy was claimed for $8,500 by trainer Richard Delp for owner Harry G. Hopkins of Darlington, Md.

Dr. Peatoppy was allowed to resume racing last week. State stewards apparently are satisfied with the explanation that the two horses had been switched inadvertently.

Today, racing for an $8,500 claiming tag, Dr. Peatoppy closed fast along the rail under Joseph Sierra to beat favored The Austrian Count going away. He paid $16.80 and topped a 10-9-2 triple worth $232.50.

Earlier in the meeting, Dr. Peatoppy, racing as Sun Dandy, had won two races for a $4,000 claiming tag at odds of 5 to 1.

Ray Stifano, trainer of Dr. Peatoppy and Sun Dandy, said before the race: "The track security people are digging and digging for dirt in this matter and there isn't any. I offered to take a lie detector test from the minute I realized that we had made a mistake. They wouldn't do it."

As result of the switch of Dr. Peatoppy for Sun Dandy, horse identifier James Rowan, a veteran racing official, has been replaced by Michael Hopkins and Coley Blind. Blind was the assistant identifier who spotted Sun Dandy as the wrong horse. Today, Blind made the identification twice before the horse was led onto the track.