Katowice is a unique finale in the WorldTour because it features a kilometre long straight downhill finish, where riders regularly record speeds of well over 70 km/h in the bunch gallops for the line.
Although official records do not exist for high-speed sprints in WorldTour events, Mezgec, 31, said he was told by the race, which organised a competition for the fastest rider with 200 metres to go, that he had clocked more than 82 km/h on his downhill blast to victory.
Mezgec’s time is 1.2 km/h faster than the previous best time for Katowice, which reports say was recorded by Jonas Van Genechten in 2014. Marcel Kittel's speed in 2010 was the previous fastest at 78.3 km/h.
"This sprint is really special. It’s such a high speed and the last kilometre is very straight. You need a bit of luck, big gears and good timing," Mezgec said afterward. "The speeds are over 80km/h an hour. I’ve got second third and fourth here, but it's a big lottery to win. You need a lot of luck in a sprint like this."
Mezgec said the organisers, on giving him his special prize as 'fastest sprinter', told him he had gone at "82 point something", and he said that he had "probably" not done such a high-speed sprint before "because this is the fastest I’ve ever done all year."
To get to that velocity, Mezgec said he took a "slingshot" off Fernando Gaviria (UAE Team Emirates), who had launched his own prodigious acceleration earlier on.
"I wasn’t watching the big names, though, because every sprint is a new game, a new lottery," he said. "I knew when I had to start, and I had to come from behind because in a sprint like this, when you are second wheel, you don’t do too much, but when you are ahead you do a lot more work than in second place."
Mezgec's win also marks his return to WorldTour wins for the first time since his 'golden year' of 2014, when the Slovenian took wins in the Giro d'Italia, the Volta a Catalunya and the Tour of Beijing. His last triumph outside cycling's top league came in his national Tour in June.
"It feels good," he said. "I’ve been trying to win for a while in WorldTour races. I don’t have so many chances because we have so many sprinters in the team.
"But yeah, I’ve been in Poland for I think seven times, and many times I’ve made second, third or fourth, so this time it all came together and I won."
Mezgec will probably go to the Vuelta a España, he said, but the competition within his team is strong.
"This win will help, sure, and I’m very motivated to be there,” he said. "The fast guys like Matteo Trentin and Daryl Impey were at the Tour de France, so probably they won’t do the Vuelta. But we always make a chance for everyone."
Regardless of where Mezgec goes from here, Sunday's win will certainly go down as one of his finest in years, and of a type – downhill – that he said will stay in his memory as a kind of sprint he has never won before.
"I’ve won sprints on downhill gradients that were maybe one percent," he said. "But on a such a downhill gradient and so fast – never."