Service holds proved a mammoth mission for McDonald in the second set. He survived a 15-minute struggle to hold before tipping momentum in his corner for his first break at 3-2.
Sinner was hanging on by the skin of his teeth when he fended off five set points on serve at 2-5 before he saved five more to break in the subsequent game in another 15-minute battle.
Having started the match with strapping beneath his left knee, the 20-year-old made a quick pit stop to have his leg worked on before set point No.11 eluded McDonald.
When the pair headed to the tie-break there was an air of inevitability.
Sinner’s elation upon stealing an 89-minute set was more akin to sealing the contest.
He had narrowly held off his opponent in their only prior clash, for the title in Washington last August, and his superiority under the pump again proved decisive.
Sinner’s second-set great escape merely emboldened him and took the wind out of McDonald’s sails as he closed it out after two hours, 51 minutes.