Watch: KSW fighter lands punch while mounted for insane KO

WARSAW, Poland - The biggest highlight of KSW's highly anticipated stadium show might've come in the second fight.

Heavyweight Patryk Tolkaczewski appeared to be en route to handing Krzysztof Glowacki a TKO loss in the first round of their preliminary bout at KSW Colosseum 2 on Saturday. Tolkaczewski was in full mount and landing ground-and-pound.

But out of nowhere, Glowacki landed a single punch that knocked Tolkaczewski unconscious, scoring one of the most devastating and unique knockouts in recent memory.

Here's the finish in real time:

And here's the replay:

Glowacki is a former WBO cruiserweight world champion in boxing. The 36-year-old squared off with current world heavyweight champ Oleksandr Usyk in 2016. This highlight-reel victory over Tolkaczewski was his MMA debut.

KSW is one of the biggest MMA promotions in Europe and the MMA leader in Poland. Colosseum 2 is its second event at PGE Narodowy, the national stadium. Approximately 50,000 fans will be in attendance - that would be a sold-out crowd - making for one of the highest attendances in MMA history. About 57,000 were at KSW Colosseum 1 in 2017.