The 25-year-old World no. 1 has been dating stunning Ms Stoll for three months and the pair spent New Years Eve together, according to Irish Media.
The Northern Irish golfer shared a picture on Instagram of two glasses of champagne at a luxury hotel in Ireland, just 12 months after he used the photosharing app to tell the world of his engagement to Caroline Wozniacki.
McIlroy and Ms Stoll, from Naples, Florida, met in September 2012 when he nearly nearly scuppered the Ryder Cup Miracle at Medinah before it had even started by oversleeping.
Ms Stoll, who is manager of Championship Volunteer Operations at the PGA of America, came to his rescue before police rushed him to the course.
The new couple have apparently been dating for around three months and, according to several Irish newspapers, saw in the New Year together at a luxury hotel in the 13th-century Ashford Castle in Co. Mayo.
McIlroy shared a picture on Instagram that night of a champagne bottle with two glasses resting on napkins bearing the hotel's logo.
Just 12 months previously, Wozniacki had been showing off a shiny engagement ring after McIlroy had popped the question on New Year's Eve.
He also had only two majors to his name and the world was wondering why his form on the course was so bad.
Since then the 25-year-old world No 1 has had rumoured romances with Irish model Nadia Forde, who went on to appear in I'm A Celebrity... Get Me Out of Here, receptionist Sasha Gale, South African model Shashi Naidoo and now Stoll.
Mclroy is back to work in preparation for his return to the course at the Abu Dhabi HSBC Golf Championship in the Emirate on January 15.
His major aim this year will be to complete a career Grand Slam by winning the Masters in April.
Should the Ulsterman claim the green jacket at Augusta National he would then have a shot at becoming the first golfer since Tiger Woods in 2001 to hold all the major titles at once when he competes in the US Open at Chambers Bay in June.
But it appears McIlroy could have found a birdie he cherishes even more than those he earns on the course in the form of his Ryder Cup heroine.
