"I can't believe it, I can't believe it. This is the toughest race in the world to win," Nafzger said.
Street Sense broke two Derby jinxes to score the win under jockey Calvin Borel, who was 0-for-4 in the race.
In beating Hard Spun by 2 1/2 lengths, Street Sense became the first Breeders' Cup Juvenile winner to return in the spring and win on the first Saturday in May, snapping an 0-for-23 skid. He did so on the same Churchill Downs track where he won the Juvenile six months ago. He was also the first 2-year-old champion to win the Derby since Spectacular Bid in 1979.
Street Sense was sent off as the 9-2 favorite on his hometown track.
The colt ran 1 1/4 miles in 2:02.17 and paid $11.80, $6.40 and $4.60 as the highest-priced winning favorite in Derby history. Smarty Jones paid $10.20 to win in 2004.
Hard Spun returned $9.80 and $7, while Curlin was another 5 3/4 lengths back in third and paid $5.60 to show.
While it was Nafzger's second win in three tries, trainer Todd Pletcher, who had a record-tying five horses, was skunked again. He is now 0-for-19 in the Derby.
Queen Elizabeth II was one of the 156,635 racing fans on hand, the third-largest crowd in the Derby's 133 years. She watched from the fourth-floor clubhouse balcony overlooking the finish line. With the sun finally emerging before post time, she had a picturesque view of the Twin Spires to her left.
Borel's Cajun accent gives away his humble Bayou origins. Asked what it was like to win in front of royalty, he said, "It meant everything in the world."
The 65-year-old Nafzger, who is nearly retired, wasn't as emotional as he was in 1990, when Unbridled won for 92-year-old Frances Genter. Because of her faltering eyesight, Nafzger called the race in her ear so she could follow her colt to the finish line.
Then he gave her a big kiss when Unbridled crossed the finish line.
This time, Nafzger's words to 83-year-old owner James Tafel were few and to the point.
"Mr. Tafel, we're clear, we're clear. It's up to him now," Nafzger said.
The moment Street Sense crossed the finish line Nafzger wrapped his arm around Tafel, shook his hand and pumped his left fist.
By the time the two made their way to the crowded winner's circle, the white-haired Tafel was beaming.
"This is the aspiration of anybody and everybody in the horse business. It's just overwhelming," he said.
Nafzger and Tafel were taking a second shot at the Derby together. Nafzger trained Vicar, who finished 18th in 1999.
Nafzger works for just two owners now, having turned the day-to-day grind of his Churchill Downs stable over to an assistant. Besides Tafel, his other client is Genter's son-in-law.
"Maybe now I can afford to retire," Nafzger said, laughing.
Street Sense has finished in the money in all eight of his career races.
"This horse has never run a bad race," Nafzger said.
Curlin finished third, losing for the first time in his four-race career.
Imawildandcrazyguy was another half-length back in fourth and Sedgefield was fifth. Circular Quay, coming off an eight-week layoff, was sixth for Pletcher's best finish.
Tiago was seventh, followed by Any Given Saturday, Sam P. and Nobiz Like Shobiz. Dominican was 11th, then came Zanjero, Great Hunter, Liquidity and Bwana Bull. Storm in May, who is blind in his right eye, was 16th, trailed by Teuflesberg, Scat Daddy, Stormello and Cowtown Cat in last.
Borel is the master of saving ground and he demonstrated that skill in the Derby as Street Sense dropped back at the start and headed for the rail. While Hard Spun shot to the lead, Street Sense tucked in 19th along the fence.
Borel still had a snug hold on the reins as Street Sense turned for home. A quarter of a mile from the finish, Borel finally moved Street Sense to the outside and they accelerated away from the pack. They quickly reeled in Hard Spun, catching him in the final eighth of a mile as Borel sneaked a peek over his right shoulder approaching the finish line.
Once they crossed it, Borel thrust his whip in the air in celebration.