Defending champion Shane Lowry began with a three-under par 69 in a solid start at the BMW PGA Championship at Wentworth.
Lowry, who triumphed in 2022 by a single stroke from Rory McIlroy and Jon Rahm, began brightly with birdies on the opening two par-threes at the second and fifth.
He moved to three under after firing his approach into 12 feet on the seventh and sinking the putt.
His momentum stalled abruptly with back-to-back bogeys on 9 and 10, missing a five-footer for par on the latter.
He recovered the ground with a two-putt birdie on the par-five 12th, following it up with another birdie on a short hole, draining a 12-footer on 14.
However, he was unable to improve on this in the closing par fives, after failing to find the fairway with his tee shots and being forced to lay up.
Lowry is five strokes adrift of leader, Denmark's Marcus Helligkilde, who struck 10 birdies en route to an opening 64.
The 26-year-old Dane, who has won three times on the Challenge Tour, bounced back from a dropped stroke on the third with a remarkable seven birdies in his next nine holes.
Following a bogey on the short 14th hole, he put on another spurt with three closing birdies to climb to eight under.
He sits two strokes clear of England's Matt Fitzpatrick and Scotland's Richie Ramsay, whose rattled in four birdies on the trot around the turn as he carded 66.
Conor Syme, Thomas Detry and Danny Willett are part of an eight-way tie for fourth on five under.
The group on four under includes Ryder Cup bolter Ludwig Aberg, whose back nine contained six birdies but also a double bogey on 17, as well Poland's Adrian Meronk, the most contentious omission from Luke Donald's team.
"The 17th was a little bit stupid but other than that I felt like I hit the ball great and gave myself a few chances, especially on the back nine where it's a little bit more scoreable," Aberg said after his round.
"Overall, I’m really happy with the way I played. I was very nervous this morning, it would have been weird if I wasn’t, and there were a lot more people following me round than usual."
Lowry was joined on three under by Ryder Cup team-mates Viktor Hovland and Tommy Fleetwood.
Rory McIlroy had an erratic morning but birdied the closing par-five 18th to post an even-par 72.
The world number two opened with a bogey after leaving his approach short of the green. He got back into red numbers with birdies on the seventh and 13th before successive dropped strokes on 14 and 15.
McIlroy, a past winner in 2014, did at least manage a birdie at the par-five 18th after his eagle putt charged a few feet by the hole.
THAT Rory ball follow into 18 🎥 #BMWPGA | #RolexSeries pic.twitter.com/4xzjVkctnG
— DP World Tour (@DPWorldTour) September 14, 2023
European Open champion Tom McKibbin recovered from a horror start to post an opening 74, racking up five birdies on the back nine to get back on track.
The Belfast-born golfer was six over after eight holes and appeared destined to prop up the field but rallied impressively on the inward nine.
Padraig Harrington is unlikely to be around for the weekend after a six-over round in which he failed to register a birdie.
