Inaugural tournament champions Jason Day and Lydia Ko face an uphill battle to catch the runaway leaders after the opening round of the Grant Thornton Invitational.
The Australasian duo, who won the event back in 2023, fired a 12-under 60 in the scrambled event for mixed teams at the Tiburon Golf Club on Friday.
They went bogey-free and had 12 birdies, but men's world No.53 Day and women's No.6 Ko still find themselves under the pump in a tie for eighth.
