Lehecka is no mug, a 23-year-old Czech who reached the Australian Open quarter-finals a couple of years ago, who's been on the verge of the top 20 and is still a force to be respected on tour at No.34.
None of which proved any defence against a supreme champion back on a mission on Saturday as Sinner gave Lehecka such a hiding that the only decent thing the crowd on Court Suzanne Lenglen could do was to rise and roar when he finally won a game at the 12th time of asking.
Lehecka acknowledged the sympathy with an ironic raised arm and fist pump. It didn't get any easier, as he eventually left the arena schooled and shell-shocked, marmalised 6-0 6-1 6-2 in just over an hour-and-a-half.
That's now 17 grand slam match wins in a row for Sinner, looking as if the only thing his doping ban provided was a welcome bit of R and R for the 23-year-old. This was his most dominant win ever at a grand slam.
"He played amazingly, the only dominator on court today, did everything right. I felt like I was playing against myself because he was a thousand times better in everything," sighed Lehecka.
"I thought I wouldn't win any games."
Sinner, who'll meet a doubtless fearful Andrey Rublev in the last-16 on Monday, said: "We try to improve.
"Today, I don't think there are many things I can improve."
No-one was arguing. He hit 31 winners, made just nine mistakes, earned seven breaks and saved the only break point he faced. Lehecka reckons only defending champ Carlos Alcaraz can beat him.
Novak Djokovic will take some beating, though, after his latest 6-3 6-4 6-2 evening stroll against Austrian qualifier Filip Misolic set him up for a date with Cameron Norrie, who won an all-British clash with Jacob Fearnley 6-3 7-6 (7-1) 6-2.
Djokovic had hoped he'd be spared the night match so he could watch the Champions League final, but his contest finished just as Paris Saint-Germain were completing their consummate 5-0 thrashing of Inter Milan. It's fair to say the locals' interest really lay elsewhere as Paris just went firecracker crazy.
The adventures of wonder boy Joao Fonseca were ended ruthlessly later on Lenglen by Britain's increasingly impressive Jack Draper, the US Open semi-finalist who tamed the 18-year-old Brazilian 6-2 6-4 6-2.
Draper still saw enough of the kid to muse: "It's just only going to go up for him. It's going to be scary what he's going to be able to achieve, for sure."
Alexander Bublik, the Kazakh maverick who sent Alex de Minaur home in a second-round sensation, continued his fun with a 7-5 6-1 6-2 dismissal of Portuguese qualifier Henrique Rocha and will meet Draper next.
Bublik had everyone chuckling as he suggested the secret of his revival may have been that he had been working actually too hard to stay in the top 20 so he decided to go off on a tip to Las Vegas instead. Not a training trip, he explained, but "a three-day hangover thing".
"I said, 'OK, let's go to Vegas'. We enjoy. We change the racquet. We did many things. I said, 'OK, if it goes, it goes. If not, thank you very much, tennis' - and it worked."
Suggesting the tour was now populated by health and fitness-obsessed "robots", Bublik's clearly proud to be anything but.
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