Unseasonal heavy rain, topped by a hailstorm, delayed the world No.1's arrival on Campo Centrale to play Francisco Cerundolo. He initially made heavy weather of the tie, the Argentine being in good form on clay this season.
But having taken the first set on a tiebreak the world No.1 eased to victory in what was his third match back since a three-month ban for a doping offence.
While Sinner was winning 7-6 (7-2) 6-3 in two hours, 17 minutes Australia's No.1 was kicking his heels. Scheduled on last on the Grand Stand Arena Alex de Minaur spent a long afternoon and evening waiting to play his last-16 tie against American Tommy Paul.
Should de Minaur win he will face Hubert Hurkacz who beat Jakub Mensik, seeded ten places higher at 20, 7-6 (7-5) 4-6 7-6 (7-5). De Minaur leads their meetings 2-1, but the Pole won the only encounter on clay, in Madrid six years ago.
Sinner's initial struggles may have given hope to de Minaur, who is seeded to meet him in the quarter-finals. The Italian has won all ten of their meetings and de Minaur will need to take advantage of any rustiness.
De Minaur followed on court defending champion Alexander Zverev, who beat Arthur Fils 7-6 (7-3) 6-1.
Zverev now plays Lorenzo Musetti who had match point against Daniil Medvedev just as the rain arrived. Nearly three hours later the pair came back on court and Musetti closed out with an inside-out forehand winner on the first point of the resumption.
Musetti, a new entrant in the top 10 of the rankings at No. 9, won 7-5, 6-4.
Before the rains came Carlos Alcaraz moved into the last eight, and a rematch with Jack Draper who defeated him in the semi-finals at Indian Wells in March.
Alcaraz was made to work for a 6-3 3-6 7-5 victory over Karen Khachanov, is fifth in five matches against the Russian.
"Physically I was struggling a little bit," Alcaraz said. "Not any pain in any part of the body. I was just tired. I had to run a lot. I was really proud the way I fought (for) every ball."
The third-ranked Alcaraz wore a long black brace that covered the upper portion of his right leg and stretched down to just below his knee.
Alcaraz withdrew from the Madrid Open last month due to an upper right leg ailment that bothered him during the Barcelona Open final. He also had a left leg injury.
Alcaraz, who won the Monte Carlo Masters in April, is now 12-1 on clay this season. The four-time grand slam champion will next face No.5 Draper, who rallied past Corentin Moutet 1-6 6-4 6-3 on the red clay courts of the Foro Italico.
Rome is the last big warm-up tournament before the French Open starts May 25.
with AP
