Of course it's happened, but saying it's because of the opening is not correct. It's because I didn't calculate well and my other skills were not good enough. In very fast time controls it can give you a big edge if you're good at memorization, but most opening lines work only in very specific circumstances and you can play maaany games before you see it.

Fairly often one player will be in a position where they are more comfortable in intermediate games, but the game is far from over.

Weaker players sometimes fall apart entirely in the opening, but unless you're in the market for the world champion title, there's absolutely no need to memorize openings. Games are decided either by simple tactics or endgame knowledge more than anything at the lower levels.