LOUISVILLE, Kentucky — Mystik Dan won the 150th Kentucky Derby in a photo finish, edging out Forever Young and Sierra Leone for the upset victory.

Sent off at 18-1 odds, Mystik Dan and jockey Brian Hernandez Jr. rode the rail down the stretch with a short lead. Forever Young from Japan and Sierra Leone gave chase and pressured the leader to the wire in front of 156,710 at Churchill Downs.

The crowd waited several minutes before the result was reviewed by the stewards and declared official.

“The longest few minutes of my life,” Hernandez said, after he and bay colt walked in circles while the stunning result was settled.

Fierceness, the 3-1 favorite, finished 15th in the field of 20 3-year-olds.

Mr. Hernandez and trainer Kenny McPeek had teamed for a wire-to-wire win in the Kentucky Oaks for fillies on Friday with Thorpedo Anna.

Mystik Dan ran 1 1/4 miles in 2:03.34 and paid $39.22, $16.32, and $10.

Sierra Leone returned $6.54 and $4.64. Forever Young was another nose back in third and paid $5.58 to show.

Sierra Leone lugged in and bumped Forever Young three times in the stretch, but jockey Ryusei Sakai didn’t claim foul.

The 150th Run for the Roses would likely be unrecognizable to the 10,000 people who attended the first Derby at an unknown track on the rural outskirts of Louisville, Kentucky.

On May 17, 1875, the date of the first Derby, Ulysses Grant was the president, the country was still reeling in the aftermath of the Civil War and patrons arrived to watch the horses by riding horses there themselves. Women required a male escort to attend, the Courier-Journal reported, and admission was as little as $1.

Now more than 157,000 pack into Churchill Downs from all over the world for a dayslong spectacle of huge hats and mint juleps, where most grandstand tickets cost more than $500 and celebrities celebrate in lavish suites high above the track.

The sun was shining Saturday, and Derby-goers didn’t have to contend with the bad news that put a damper on the race last year, when seven horses died in the week leading into the race. They posed for pictures in front of a sign commemorating the anniversary and whispered about the celebrities who made an appearance.

Kentucky native Wynonna Judd was at the track to sing the National Anthem. Martha Stewart was the day’s grand marshal, charged with saying “Riders’ Up!” to start race.

Travis Kelce, three-time Super Bowl champion and Taylor Swift’s boyfriend, comedian Jimmy Fallon, and musician Kid Rock were also at the track.

Patrons jockeyed to watch the horses get saddled at the track’s renovated new paddock, now a massive horseshoe-shaped space at the foot of the famous Twin Spires.