By Mark Lamport-Stokes

ARCADIA, California (Reuters) - A stunning victory by 6-year-old mare Beholder in the final race of her career and another win for record-setting jockey Mike Smith stole the limelight on the opening day of the Breeders' Cup on Friday.

With Gary Stevens on board, Beholder upset the even-money favorite Songbird in an epic charge down the stretch for the $2 million Breeders' Cup Distaff, neither horse giving an inch until Beholder triumphed by a nose in a photo finish.

Beholder, who was scratched from last year's showpiece Breeders' Cup Classic because of illness when fancied as a chief rival to the eventual winner American Pharoah, ended her illustrious racing career with 18 wins from 26 starts.

"I think she had cemented her place in history prior to 2016, and she just added another star to it today," Stevens said of Beholder, who started the Distaff as a 3-1 shot.

"I've just never seen a racehorse stay at this peak form, especially a filly. The show that those two (Beholder and Songbird) just put on is worth the price of admission for everybody that showed up today.

"This was horse racing at its best. She (Beholder) laid her heart out there on the racetrack and gave me absolutely everything that was running through her veins."

The one lowlight came when Argentina-bred Corona Del Inca had to be euthanized after fracturing her right front leg during the Distaff.

The 5-year-old mare, who had been reluctant to enter the starting gate, was pulled up at the top of the stretch by jockey Pablo Falero, had her leg splinted and was then taken to the track's equine hospital for further evaluation.

"Sadly the radiographs ... revealed that she had a much more serious injury than it was apparent on the racetrack," on-call veterinarian Dr. Scott Palmer said in a statement.

"The nature of these injuries was so severe that there was no way she could be kept comfortable nor the prognosis be good for treatment. For those reasons she was euthanized."

Earlier in the day at a sun-bathed Santa Anita Park, Hall of Fame jockey Smith expertly guided Tamarkuz, an 11-1 shot, to a come-from-behind victory in the $1 million Dirt Mile to extend his Breeders' Cup record to 23 race wins.

Tamarkuz surged past Gun Runner in mid stretch to win by three-and-a-half lengths with Accelerate a neck behind in third and odds-on favorite Dortmund fourth.

"He (Tamarkuz) didn't break real sharp, but Mike did a great job with him settling back, and Mike's just a great rider," said trainer Kiaran McLaughlin. "It was just a great trip."

(Editing by Andrew Both)