King Of Leogrance has recorded an emotional win for the Danny O'Brien stable in the 150th Adelaide Cup at Morphettville.

Earlier on Monday, a track rider from O'Brien's Thirteenth Beach stable near Geelong was killed when he and the horse he was riding were struck by a car.

The driver and horse were reported to have minor injuries.

Representing O'Brien in Adelaide on Monday, assistant trainer Ben Gleeson was fighting back tears after the Lloyd Williams-owned King Of Leogrance won the Group Two 3200m-race.

"It's a very tough day for the whole stable," Gleeson told broadcaster racing.com.

"We're very happy for the Williams team but with everyone back home at Barwon Heads and Flemington, it's been devastating.

"We're really hurting and we appreciate everyone's support today."

Earlier in the day, Melbourne Cup-winning trainer O'Brien expressed his heartache in a statement over the loss of the stablehand, believed to be a Japanese national.

"Our thoughts, prayers and support are with the family of our friend and colleague and all our team," O'Brien said.

"We are completely heartbroken.

"We have had some tough days in this industry, but they are nothing compared to the heartbreak and sadness of today."

Sent out the $2.20 favourite under Damian Lane, King Of Leogrance cruised to a 2-1/4 length win from Good Idea ($17) with Chouxting The Mob ($31) three-quarters-of-a-length away third.

King Of Leogrance's win was the third of the day for the O'Brien stable after War Tiger won earlier on Monday's program at Morphettville and Serengeti was successful at Ballarat.

Williams' son and part-owner, Nick Williams, said Monday's success would hopefully put some cheer into the O'Brien stable after a shocking day.

"I think this goes out to all the staff at Danny O'Brien's," Williams said.

"Obviously it can't make up for what has happened this morning, but hopefully it cheers them up a little.

"It's a horrific thing to happen but thankfully this horse has shown his true form today."

Williams said King Of Leogrance could possibly head to next month's Sydney Cup (3200m) at Randwick.

"It's only his third run in this time so we might look at going to Sydney with him," he said.

Lane said there was no ceiling to King Of Leogrance, a French-bred import.

"He's such a progressive type that no matter what they set him for, whether its a Sydney Cup or the Andrew Ramsden and try and get him into the Melbourne Cup, he would be suited," Lane said.

O'Brien won last year's Melbourne Cup with Vow And Declare.