Answer
47. Nf6+!!
It's checkmate in 2 in one of two ways.
47...Qxf6
48. Qg4#
47...Kh4
48. Qh3#
https://www.chess.com/analysis/game/live/97535431411?tab=analysis
It's a speed chess game I just watched. Let me know if I screwed this up. I can't copy and paste from the site.
I was so fixated on how black was going to win - I didn't see the danger at all. I only knew black was toast due to the evaluation bar suddenly indicating mate in 2.
[Edit - I fixed a mistake]
Do you play endgames against an engine? That's what I do at chess.com. I leave the evaluation bar on so I can get immediate feedback. That's very lazy but it makes it more fun.
I could go back through my games and do that to see where I lost my advantage. Great idea! Thank you
That's certainly an option. What I do is play though other people's games. For me personally - going through my own games is no fun at all. But whatever works and keeps it fun is key.
Physical contests like MMA stamina is something that some fighters skimp on. I've always been kind of amazed how many fighters don't fully understand how important stamina is. I think of endgames being the "stamina" of chess.