Clark opened with a run of five birdies in nine holes and ended the day bogey-free on 63, while Fitzpatrick started and finished with birdies to follow closely behind.
It was three years to the day since Northern Ireland’s McIlroy lifted the trophy, with the pandemic cancelling the last two years of the championship.
On Thursday he finished with a round of 66 tied with Tony Finau, Lee Hodges and Mackenzie Hughes.
In 2019, McIlroy carded a stunning final round of 61 at Hamilton Golf and Country Club to seal a seven-shot triumph.
Last month, Fitzpatrick missed out on his first major title by two strokes in the US PGA Championship at Southern Hills.