Preflop: first off, i think in a 7 handed game vs. a maniac's UTG range KTs is probably barely profitable to play in position, but to realize that profit you should raise instead of flat. this is very nuanced and a matter of personal preference where the minimum requirements to flat are, but I'd probably be flatting with a range of 22-99 and Ace rag suited and KQ. I might flat with KJ or I might 3bet with it. I'd definitely 3bet AK/AQ for value and TT+ and I'd be 3betting a few more
hands to balance the value range. hands like KTs are good candidates because they play easier heads up with the betting lead. anyways, that's just for future reference because you flatted and I don't think it's TERRIBLE by any means, just maybe not the MOST +EV line.
Flop: clearly a good flop, but we're either way ahead or way behind. and it's 3 handed so I'm looking to pot control and re-evaluate. obviously we have no problems calling the maniac with TP. when the button comes along we should be somewhat worried that we're outkicked and we might consider folding later, only because of the button.
Turn: BINK! now kicker's don't matter and we have the essential nuts except for 88. if he has 88 that's just a cooler. we basically can't worry about losing and must focus instead on extracting. Id be expecting to chop the pot with the Button a fair amount of the time, so all of the profit will come from the maniac. so it's important to keep the maniac in the hand. raising will let him off too easy if he's
bluffing or just has a smaller pocket pair or just has a single 8.
River: when maniac bets 300 into 1,830 he probably has nothing but flatting is ideal because if we raise he'll probably only call with an 8 or K and so we either lose or chop when we raise (not good). so flatting his tiny bet is fine. Now, when the Button raises what can he have that would be beating us? just a single 8 and that's surely in his range but is every combo of 8x in his range? probably not. probably just 78s,89s,8Ts,8Js,8A and maybe 68s.. Is a single K in his range? (only 1 remains) I think so because he probably also puts you on a K and is trying to
bluff you off a chop (I give him this much credit because it's a play I would make and you say he's played for a long time. bluffing your opponent off a chop is an essential skill to turning a long term profit). Which Kx hands are in his range? maybe AK (he might 3bet pre), KQ,KJ,KT,K9 so probably more combos of Kx than 8x because most of his 8x combos would need to be suited to be playable and fewer of his Kx combos need to be suited.
blah blah blah you have the 2nd nuts and you're getting almost 4:1 on a call and he is a good enough player to be bluffing you off a chop. he only has to be bluffing or chopping 20% of the time for calling to be break even or profitable.
