Deep Field's first Group One test didn't go to script with trainer John Hawkes admitting it was impossible to find an excuse for the previously unbeaten sprinter.

Deep Field was sent out the $2.15 favourite but couldn't quicken with Lankan Rupee which raced clear to win the Lightning Stakes by 2-3/4 lengths.

Three-year-old Brazen Beau finished strongly to relegate Deep Field into third.

Hawkes offered no excuse for Deep Field which had won his first five starts and was making his autumn carnival return.

"He wasn't good enough on the day, simple as that. The other horse was too good," Hawkes said.

Owner Alan Bell said Deep Field raced below expectations.

"I can't explain how he found nothing but we'll just have to work out what the situation is, I suppose," Bell said.

Bell said connections would have to see how the four-year-old comes out of his first defeat before deciding the sprinter's next move.

"We'll just see how he is. We have to sort of regroup," Bell said.