On a day when the Italian, already one of the sport's greats at just 24, prevailed, there was also a reminder at another ATP 500 hard-court event in Basel that he could soon be challenged by brilliant Brazilian teen Joao Fonseca, who won the Swiss Indoors title.
With his 6-3 6-4 win over Alejandro Davidovich Fokina in the title match, the 19-year-old Fonseca became the third-youngest ATP 500 champion in the series' 16-year history.
In a blockbuster Vienna final, Sinner, who'd beaten Zverev in straight sets at this year's Australian Open final, won his 21st consecutive match on indoor hard-courts as he notched his 22nd tour-level title.
The world No.2, who had knocked out Australia's No.1 Alex de Minaur in the semis, banged down 11 aces and unleashed 44 winners in a thrilling contest that lasted two hours and 28 minutes.
"It feels amazing," Sinner said, after he had suffered a struggle with cramp in a tight deciding set.
"It was such a difficult start in the final for me. Down a break ... I had some chances in the first set, couldn't use them. He was serving very well.
"I tried to stick there mentally. Trying to play my best tennis when it counts. Third set was a bit of a roller-coaster. Very happy to win another title. It's very special."
After sharing the opening two sets, the third proved gripping. Sinner was clearly ailing with cramp in his left hamstring during the seventh game, but refused to back down.
Zverev briefly looked set to seize victory after edging ahead 5-4, but Sinner dug deep to level the match before producing a crucial break for 6-5 and then serving out the match for his second Vienna title.
"Yeah it was very difficult, of course," Sinner said.
"Most important is trying to not give up. Trying to stay there. Trying to see what the situation is. I just tried to make the right choices at the right time. I think that was the key today.
In Basel, Fonseca dedicated his trophy to his mother. "Since I was young, my mum travelled with me. Since I was 11, I only travelled with her, so that title is for her," he said after his 86-minute win.
After he had beaten Jaume Munar in the semis, his folks got a late flight to make the final.
"My parents just came from Brazil. They were coming to Paris and changed their flights and came here one hour before the match with my uncles," Fonseca explained.
"It is just amazing to have them here for the biggest title of my career."
It was his second tour-level title, and Fonseca will rise to a career-high No.28 in the rankings.
