Last year's runner-up Sinner, the overwhelming favourite against the unseeded Cerundolo, called it quits as a result of foot blisters when trailing 4-1 in the first set.
Italian Sinner's nightmare blisters meant world No.103 Cerundolo's dream run continued, as he reached the semi-final in his first Masters 1000 main draw.
"I didn't know anything," Cerundolo said in his on-court interview.
"When I was serving at 3-1, 30-0, I saw him bending down. It was really strange.
"I didn't see anything wrong and I hope he is OK, he is a great player."
The 103rd-ranked Argentine battled past Americans Reilly Opelka and Frances Tiafoe and Frenchman Gael Monfils earlier in the tournament and now faces the victor of a meeting between German second seed Alexander Zverev and world No.8 Casper Ruud of Norway.
"It means a lot (to advance). It is everything I have dreamed of," Cerundolo, who had an 0-2 main-tour record on hardcourts before this tournament, said.
Cerundolo, 23, who reached his maiden tour-level the final in Buenos Aires last year, has enjoyed a strong 2022 campaign, winning an ATP Challenger Tour title on clay before soaring into the semi-finals in Rio de Janeiro.
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