World number 354 Jacob Skov Olesen of Denmark shot a serene four-under-par 67 to take the early British Open first-round lead in tough conditions at Royal Portrush on Thursday.
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The 26-year-old left-hander eagled the 12th hole and picked up four birdies before a bogey at the last left him joint top of the leaderboard alongside England's Lee Westwood, one ahead of China's Li Haotong.
Dane Nicolai Hojgaard, who went out in the first group of the day, compiled a solid 69 to finish at two under.
"I had to grind pretty hard to shoot a score today," he said. "I felt like I squeezed the most out of it, and sometimes those days are really nice to have."
Veteran American Phil Mickelson, the 2013 Open champion carded 70, including a spectacular par-save when he holed out from a greenside bunker.
World No 1 Scottie Scheffler was one under after five holes, level with Ireland's Shane Lowry who won the Open at Royal Portrush in 2019.
Northern Ireland's Rory McIlroy is among the late starters as he bids for a second Claret Jug in the company of England's Tommy Fleetwood and American Justin Thomas.
Ireland's Padraig Harrington, twice Open champion, struck the first tee shot of the tournament in cloudy conditions with thunderstorms forecast to hit the course in the afternoon.