I have two that stand out for me.
One was at a small proxy tourney a few years ago. I was playing vs some kind of Storm deck with my Oath of Druids. I kept a hand with FoW+Blue, Mox, land, Tinker, Yawgwill, Voltaic Key, blank.
I counter his first attempt to go off and put down the Key, but fail to draw mana while he draws nothing but mana. Eventually, both of us drawing blanks for what feels like forever, he hardcasts (!) a Darksteel Colossus, and starts beating down.
At six life, I draw what I thought would be my last card - a mox Sapphire. I think for about five minutes, before coming up with the correct sequence here: Play Mox, Cast Tinker for Lotus. Sac Lotus for BBB, cast Yawgwill. Recast Lotus, Mox from 'yard, Recast Tinker using Lotus mana for Time Vault, activate with the mana from the re-played Mox for infinite turns.
That was the first time I realised I was actually capable of finding small holes like this to eke out a win.
The other one was even better. It was sometime after that, and I was playing Two Card Monte vs Gush Storm. My opponent had succesfully gotten rid of Leyline and managed to kill a Helm. I had a Welder, an artifact, and an untapped Ancient Tomb in play, when he begins to storm off. Ritual, ritual, ritual, Demonic for Yawgwin, recast the rituals, recast demonic. At this point I say: "Hold it, I want to respond. Tap Welder, sac artifact, to get my Helm back in play, tap Tomb to activate it for 1. Ok?" He thinks for a minute, shrugs, then tries to put a card in his 'yard. At this point I say, "hold it, your deck is now removed from game.", and he goes "What?" "Read Yawgmoth's Will. It Leylines you..." He looked so dejected after that, I actually felt sorry for him.
But yeah. I won a game, and the match, because my opponent resolved a Yawgwin. How often has that happened in the history of Magic?