I'm on my laptop so I don't have the screenshot, but I'd have to go with the time when I first beat Unreal Tournament on Godlike, and I beat Xan Kriegor (pretty much the boss of the game) in the 1v1 Deathmatch 15 kills to negative 1. Long story short he did kill me once but I knocked him off into space twice (and a suicide counts as -1 frag.)
I had originally had so much trouble, I looked worse than this [http://www.youtube.com/watch?v=Xi8fiw_DkzI] guy who at 3 minutes in is losing negative 1 to 5 kills.
I spent a long, long time practicing it. Learning the intricacies of the AI, how to beat an opponent who aims perfectly, and such. It took me a while, but I got it. And I was proud of myself.
For future reference, the shield belt respawns in about 55 seconds, and the armors come back every 28 or so. I used the game clock and timed them to the exact respawn. I'd be on top of where it spawns when it comes back, so I always had a health advantage. Even though he aimed perfectly, it didn't matter, because he needed 4 shots to my 2 in order to kill him.
Also, with rockets, grenades, ripper blades, flak secondary shells and bio-goo (lol biorifle/goo gun), I was able to maintain some area-control and force him to not come through a certain hallway because he would take too much damage on the approach to me. If he didn't have a clear shot he wouldn't take it, but ripper blades bouncing off walls and biorifle shots land-mining an area would stop him from advancing. So I was able to hold him off while I waited for the item respawns.
Focusing on all that, my aim improved as well, so most of my kills on him were with the shock rifle ironically enough.
Bottom line is, I learned my duel fundamentals from a Godlike AI, and then beat him at his own game, and those concepts behind duel of timing the armors/items, controlling where the enemy can and cannot go, predicting their movement and actions, going after them when they are "Fresh" and don't have a "Stack" of health/armor/weapons, all of this still applies in professional games of deathmatch, and I proudly worked on it and learned it to a limited degree by myself over the course of like a week instead of trying to find some simple "Win-easy-and-right-now" guide online.
edit:
If you actually watch the "this" video, skip to 1:04.