McIlroy, a four-time major champion, shot an approach shot for an Eagle on his way to a 4-under 67.
McIlroys second shot, from 115 yards on the par-4 3rd hole, was his best shot. He had only made one birdie in his first nine holes. McIlroy was delighted when the ball rolled in and he raised his arms in joy as he watched from further back.
Fitzpatrick was one shot ahead at 5-under through 15 of the holes when play was stopped because it was dark.
McIlroy finished at 5-under for his seven final holes.
Lightning caused delays in play for an hour. Conditions remained blustery throughout most of the day.
McIlroys tee shot on the par-5 626-yard 18th was impacted by high grass. He chipped into the fairway, before finally sinking a 20 foot putt to save par.
McIlroy was first and second in McIlroys previous two tournaments: the Tour Championship in Atlanta, and the BMW PGA Championship Wentworth, England.
From Sept. 29th to Oct. 1st 2023, Marco Simone is the third European venue to host the Ryder Cup. This follows Valderrama in Spain (1997), and Le Golf National (2018).