DEL MAR, Calif. (AP) — Arrogate and Gun Runner square off again in the $6 million Classic on Saturday, the marquee event on the second day of the Breeders' Cup, which is being run for the first-time at Del Mar.

The 13-race, season-ending championships started with four races Friday. Nine more will be run on Day 2.

The event culminates with the Classic, the biggest event in the history of the seaside track north of San Diego.

Arrogate, the defending champion, is winless since the $10 million Dubai World Cup in March. He'll need to be in peak form to handle Gun Runner, the 9-5 favorite.

Arrogate, the 2-1 second choice, is one of four Classic entries for Baffert, who has won the race the last three years with Bayern in 2014 and Triple Crown winner American Pharoah in 2015.

The all-time richest horse with earnings of $17.3 million, Arrogate followed the Classic victory with triumphs in the $12 million Pegasus World Cup and in Dubai.

Then things went south.

The 4-year-old gray is winless since his return from the Middle East. He was a badly beaten fourth as the 1-20 favorite in the San Diego Handicap, and second to stablemate Collected in the Pacific Classic in August over the same Del Mar track.

"I think a lot of it is the way I prepared him," Baffert said. "I take the blame for him getting beat the first time. The second time, it looked like he wasn't going to run and all of a sudden he started running at the end.

"I think he should run well."

Arrogate beat Gun Runner by 2 1/4 lengths in Dubai. It's been a dramatically different story since then. Gun Runner reeled off dominant wins in the Stephen Foster Handicap at Churchill Downs and in the Whitney and Woodward Stakes at Saratoga.

Trainer Steve Asmussen, who won the 2007 Classic with Curlin, marvels at the resilient 4-year-old colt.

"This is a testament to Gun Runner and the year that he's put together," Asmussen said. "You look at what he's done this year and it's very impressive. His inner fortitude, his strength and his confidence has allowed him to do it."

Baffert conceded: "Gun Runner is the horse to beat."

In addition to Arrogate, bidding to join Tiznow (2000-01) as the only consecutive Classic winners, Baffert sends out Mubtaahij (12-1), Travers winner West Coast (6-1) and Collected (6-1).

Leading Irish trainer Aidan O'Brien has two runners in the Classic: War Decree (30-1) and Churchill (15-1).

Completing the Classic field are Pavel (20-1) and pair of 30-1 shots: Win the Space and Gunnevera.

In Saturday's other races:

— Europe sends a strong contingent to the $4 million Turf, the second-richest stakes of the weekend. Early 7-2 favorite Ulysses was scratched upon the recommendation of the track veterinarians on Saturday night. Defending champion Highland Reel will likely be the new favorite.

— The road to next year's Triple Crown starts with the $2 million Juvenile. Bolt d'Oro (9-5) is unbeaten in three starts, and likely one of the shortest prices of the weekend.

— Moonshine Memories (7-2) puts her 3-for-3 record on the line in the $2 million Juvenile Fillies.

— At five furlongs, the $1 million Turf Sprint is the shortest Cup race. It should be an all-out scramble with filly Lady Aurelia (5-2) favored to beat the boys.

— Unique Bella (9-5) has reeled off five straight wins heading into the $1 million Filly and Mare Sprint.

— Lady Eli (5-2) has overcome laminitis, a sometimes fatal hoof infection, to resume her brilliant career. The Filly and Mare Turf is her last race before retirement and a deep spot against 13 seasoned rivals.

— Defrong (5-2) defends his title in the $1.5 million Sprint against some of the fastest horses in the world.

— European star Ribchester (7-2) is 3-2-1 in six starts this year. Victories in Group 1 stakes England and France make him the one to beat in the $2 million Mile.