Daniel Brown carded the lowest round of his DP World Tour career with a 64 to take a two-shot lead after day one of the ISPS HANDA World Invitational presented by AVIV Clinics.
The Englishman carded an eagle and six birdies with a single bogey at Castlerock Golf Club to get to seven under at the event co-sanctioned by the LPGA Tour and Ladies European Tour where full fields of men and women play across two courses over the four days.
Italian Gregorio De Leo challenged Brown for the round of the day with a five-under 65 at Galgorm, where scoring proved tougher on the opening day.
English duo Callan Barrow and Alex Fitzpatrick and India's Manu Gandas were also at five under after all carding rounds of 66 at Castlerock.
It has been a long road to the DP World Tour for Brown, who is playing his rookie season at the age of 28 after coming through the Qualifying School.
He made his debut at the 2015 KLM Open but did not make another appearance until this season, as he spent time moving between the EuroPro Tour and European Challenge Tour, finishing 30th on last season's Road to Mallorca.
An excellent start to his DP World Tour career saw him make his first 13 cuts with two top tens and while he then missed three weekends in June and July, he achieved his first PGA TOUR top ten last time out at the Barbasol Championship.
That saw him enter this week 74th on the Race to Dubai Rankings in Partnership with Rolex, and he made a fast start in Northern Ireland, birdieing the second, third, sixth and seventh to turn in 31.
A birdie at the 11th was followed by an eagle at the 15th and while he bogeyed the 16th, Brown picked the shot back up at the last.
"I felt like this week more than any other was important to get off to a good start with some bad weather forecast tomorrow," he said. "There’s going to be times where you're grinding it out and battling to make pars. I've given myself a nice little buffer really ahead of that challenge tomorrow.
"It's probably as good as I played all year. Tee to green and was really solid. Holed out nicely inside ten to 12 feet and the front nine wasn't too windy but then it really got up on the back nine.
"The round just kept on flowing even though the conditions got a bit tougher so it was positive after a good three or four weeks off in the schedule."
He added: "I didn't actually get to play the Scandinavian Mixed, but I think it's a great change to the atmosphere, watching how everyone goes about things. Trying to learn off each other and also amazing for the fans as well."
De Leo - a Challenge Tour rookie making his first DP World Tour appearance - started on the tenth at Galgorm and birdied the tenth, 12th and 16th before bogeying the next.
A brilliant second to six feet brought an eagle at the 18th and he shared the lead with gains at the first, fifth and seventh before a bogey-bogey finish.
Fitzpatrick - a recent winner on the Challenge Tour - had set the early pace with five birdies in a row from the 11th but he bogeyed the first before picking the shot back up on the ninth.
Barrow also carded six birdies and a bogey in just his third DP World Tour start, as did 2022 TATA Steel Professional Golf Tour of India Order or Merit winner Gandas.
Last week's Challenge Tour winner Sam Bairstow, Swede Niklas Lemke, Frenchman Joël Stalter and South Korea's Jeugnhun Wang were then all at four under having played Castlerock.
Lemke's 67 contained a two on the par-five 15th which was the sixth albatross of the season.
English duo Todd Clements and Matthew Southgate, Spaniard Angel Hidalgo and Frenchman Robin Sciot-Siegrist were then at three under.
In the women's event, there was a four-way tie at the top with England's Gabriella Cowley, Australian Karis Davidson, Swiss Kim Metraux and Swede Ellinor Sudow all at four under.
