On a day when Shane Lowry and Rory McIlroy had to settle for 70 and 72 respectively at the Kilkenny venue, Forrest carded seven birdies as he signed for a six-under-par 66.
The splendid effort left him just two shots off lead, held by Australian Lucas Herbert after the 2020 Omega Dubai Desert Classic winner opened with a nine-birdie salvo to sit one ahead of American Johannes Veerman.
“It makes such a difference,” said Forrest of fans starting to return at European Tour events after events had been played behind closed doors since the circuit came out of its Covid-19 lockdown just under a year ago.
“Just having some people out there, just hearing the claps, and obviously some groups will have big crowds, it makes all the difference I think.
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“I definitely prefer it. I think it just helps you kind of get up for it and feel like you're absolutely competing a bit more than if it’s just dead and silent out there. I really struggled with it.”
The 28-year-old, who finished 14th in this event when it was part of the Rolex Series in 2019, has been blowing hot and cold this season.
He reckons some “stress-free pars” had contributed to this encouraging effort and is looking for more of the same in an event that has three Open spots up for grabs.
“Obviously they are a couple of pretty big weeks for us,” said Forrest of similar rewards being on offer in next week’s Scottish Open at The Renaissance Club. “Just happy with the way my game's starting to go now.”
After mixing three birdies with three bogeys, McIlroy sits in a tie for 89th spot. “Just one of those days nothing happened,” he said. “I was stuck in neutral for most of the day.
“Going to go work on a few things on the range here in a minute and see if I can start a bit better tomorrow.”
Richie Ramsay was next best among the Scottish contingent as he opened with a bogey-free 67, one better than Scott Jamieson and two less than Connor Syme.