While the weather on Sunday morning in Carnoustie was warm and sunny, the wind that can be so unsafe here has finally picked up and conditions are set to be tougher over the afternoon.
The American star started the day level on nine under par alongside compatriots Xander Schauffele and Kevin Kisner and he is hoping for a repeat of his victory at Royal Birkdale 12 months ago, although there is a large chasing pack ready to pounce, with Tiger Woods right in the mix.
The former world No 1 failed to close the gap on leader Kevin Kisner during his second rounds as he hit a second consecutive par 71.
McIlroy and Justin Rose, with five majors and an Olympic gold between them, both eagled the 14th to eventually post the clubhouse lead. At one point, there was a six-way tie at the top.
Yet amid the drama and the din, Molinari held his nerve to win by two.
Tiger Woods signalled his intent on the final day of the British Open at Carnoustie with a birdie at the fourth to move to six under par for the championship.
Brooks Koepka of the US watches his hshot from the 5th tee during the third round of the British Open Golf Championship in Carnoustie Scotland Satur
Perhaps we had no right to demand more from Woods in his return here after three years and four back operations, and his 71 for 279, three behind the victor, was not bad in this company and these circumstances. His last bogey fell on the 17th. He and millions of others dreamed of him winning a 15th major, his first in a decade, but a mid-round collapse did for Woods, decked with his hands nearly on the title. A first for Italy, too.
Francesco Molinari claimed his first major title after a sensational display at The Open on Sunday, his eight under par leaving him two strokes clear of his nearest rivals. They couldn't match it. He became the first Italian to capture a major championship. He has two seconds during that time.
Woods played his "one bad swing" at the 18th, but lady luck intervened to keep his ball out of Barry Burn and in thick rough that at least gave him a shot.
Spieth and Schauffele have parred their first two holes.
However, just as Woods threatened to grab the headlines, he double-bogeyed 11 and dropped another at the next. He couldn't muster it, though, slipping to a 74 and that four-man band in second.
The 147th Open Championship provided all of the thrills any golf fan could ask for in a major, but when a leaderboard full of major winners started to slide, only Francesco Molinari was able to string together pars and hang on at the top.