Belgium’s Thomas Detry took a one-shot lead after the first round of the AT&T Pebble Beach Pro-AM as Rory McIlroy suffered a dramatic late-round collapse.
McIlroy, playing his first PGA Tour round of the year after a win and a second place in Dubai, was leading after 14 holes as three successive birdies took him to six-under-par.
But the world number two dropped five strokes in his final four holes at Spyglass Hill – one of two courses being used by the 80-strong field – including a triple bogey at the par five seventh hole after he fell foul of a rule change which cost him a two-shot penalty.
Having dropped within a club length of an unplayable lie, he was informed before signing his card for a final 71 of a change in the rules that a player must drop on the direct line.
“I wasn’t aware that that rule was changed again in 2023, so I took a drop thinking of the 2019 rules when everything was sort of changed, said McIlroy, who trails Detry by eight strokes.
The Belgian started and finished with three birdies carding a career-high ten birdies and a career-low round 63 on TOUR. American Patrick Cantlay lies one shot behind.
Matthieu Pavon, who won last week's Farmers Insurance Open, was a shot further back on 65 after the best round of the day at Pebble Beach.
Justin Rose birdied his three holes at Spyglass Hill in a four-under-par 68, one better than fellow Englishmen Tommy Fleetwood and Matt Fitzpatrick.
Nick Dunlap, playing his first round as a professional after winning The American Express tournament as an amateur last month, was tied for last place after a four-over-par 76.
The AT&T Pebble Beach Pro-Am is the second Signature Event of the 2024 PGA TOUR Season and only Signature Event that has a set field size (due to the pro-am format). The event features no cut and is played on two courses (Pebble Beach Golf Links and Spyglass Hill Golf Course), with the pro-am portion concluding on Friday.