Amid a party atmosphere, chilled champagne flowed. Flowers and feathers on fancy hats glistened in the afternoon sun.

Jockey Tiago Pereira leds his horse Hawk’s Eyes to a win in the first race.

Thursday was Opening Day of the 75th annual Del Mar Thoroughbred Club Racing seaon with a $100,000 purse for horse owners and cash prizes for hat-wearers.

The 20th annual Hats Contest attracted dozens of men and women with wide-brimmed headwear adorned with flowers, horses, miniature replicas of the grandstands, trophies and chickens. The contest featured categories like Best Racing Theme, Funniest/Most Outrageous, Most Glamorous, Best Flowers/All Others, and Best Fascinator — a wool, lace or feather alternative to a hat.

Stands were filled with locals and out-of-towners getting their first glimpse of the enlarged racetrack. More than 45,000 spectators were expected.

Lucia Arnaz, daughter of Lucille Ball and Desi Arnaz, was on hand to present flowers to the owners of a winning horse. A photo of Arnaz’s parents hangs in the lobby of the grandstands.

The race season runs through Sept. 3. This year, a 15-date mini-season will be held in November.

“Our fall race meeting starting this year will be totally separate from our summer session,” said Del Mar Thoroughbred Club president and CEO Joe Harper. “They will be two different animals. We know our summer meet is a winner — we’ve proven it over and over again. And we expect our autumn run can be special, too, in its own way.”

The annual highlight of the summer racing season, the $1 million TVG Pacific Classic, is set for Aug. 24.

Races are scheduled Wednesday through Sunday, with the first-race post time at 2 p.m. most days. On Fridays, the first post is 4 p.m.

Admission prices after opening day will be $10 for the clubhouse and $6 for the stretch run on all other days.

The North County Transit District is operating two additional southbound trains today, one of which left the Oceanside Transit Station at 11:30 a.m. and the other set to head out at 6:35 p.m. During the season, the agency will offer a “Pony Express” ticket, which for $11 includes round-trip fare on the Coaster and Sprinter trains, along with the Breeze bus, plus stretch run admission and a free shuttle between the Solana Beach Coaster station and the racetrack.

The racing season traditionally begins on Wednesday but was pushed back a day to prepare the track following the San Diego County Fair.

— City News Service contributed to this report.