Portugal had been in good form heading into this tournament and optimism among their sizeable following in Leipzig was high that they could add to their 2016 European Championship win.
That confidence looked well placed as they dominated from the outset of this game, keeping the Czech Republic pegged back.
However, they struggled to turn good build-up play into chances and the few they managed were well dealt with by goalkeeper Stanek.
Ronaldo was the focal point of Portugal's attack and, while his contribution in general play was limited, he did have two of his side's best chances in the first half but was denied both times by the Czech keeper.
When he sent a trademark free-kick tamely at Stanek in the second-half before he was ruled offside when Jota turned in his cross late on, it looked like it wasn't going to be his or Portugal's night.
But they showed the sort of determination their fans believe will take them far in Germany to take the three points deep in stoppage time.
In what is proving a growing theme of this tournament, it was another young star who delivered the winning moment as 21-year-old substitute Conceicao slammed home from close range.