Hard to say for sure without more villain info. But I'm confused by your HH and am surprised nobody caught it: The preflop part of your HH indicates you're in the BB ("Hero is in BB with..." and "Folds around to Hero..."), but the postflop action has you in position behind UTG and UTG+2? Then on the river you're OOP again?
Whether you're IP or OOP makes a big difference here. Flatting OOP with a minraise and a call in front of you with such an easily dominated hand is dangerous. You get sucked in by the nice
pot odds, but when you catch it sets you up for hard decisions. It's best in a DON to preserve your chips for reasons I'll point out below. Note I didn't say be a nit, because IMO that's a hugely exploited tendency in a lot of DON players. But if you're going to play a vulnerable hand like this, you need to do so from position. From your HH I can't tell if you had position or not. First hand of a DON is generally not where you want to be playing bloated pots with marginal hands like A9o, especially OOP in 9-max games (I'm assuming 9-max since Merge killed 6-max DONs as I recall).
So, OOP it's a fold preflop. But let's say you're OTB and are trying to see a cheap flop IP. A9o is a hand that doesn't play well post flop, so you really need to narrow your villain's range. On the flop, TPTK might look good, but your TP isn't all that great. Had you raised the flop, villain would have called or maybe even come over the top, which should have slowed you down by narrowing villains range to overcards, overpairs, sets, and nutty flush draws.
As played, when you bink the turn with T2P, it's going to be hard for most players to get away from, especially when the river blanks like it did here. When villain comes over the top of your river bet, sure it could be a busted flush draw, but that's more likely in a cash game than DON where people are inclined to be tight and conservative with their chips. This is a pretty classic WA/WB (way ahead/way behind) situation. 53 should never show up in this spot (although I've seen such nonsense), which leaves me thinking I'm against a set, but also possibly AK/AQ type hands if villain is particularly reluctant to lay those down. So by playing such a marginal hand (especially if OOP), you've set yourself for a difficult decision when blinds were low and stacks were deep.
6-max DONs are my bread and butter these days. A successful DON strategy is quite different from a successful SNG strategy, so even a good SNG player can make a lot of mistakes if he doesn't adjust.
Of course, like anything else, the commonly accepted strategy -- when applied too rigidly -- can be exploited. So the more successful DON players are looking to exploit 2 kinds of players: the players new to DONs who are playing standard SNG strat, and DON regs who are playing a robotic nitty DON style (which generally is very tight and risk averse on the bubble). A good DON player is constantly adjusting to both of these styles.
If I can impart a single nugget of DON strategy without getting too deep, it would be to exploit overly tight players by stealing a lot, especially from OTB and SB, while avoiding those few players who will play back at you until you have strong hands. You're goal should be to build a 3K stack as soon as you can, and in the early stages players are so tight they'll let you steal them blind which puts you well on your way to 3K. With 3K you are guaranteed the win. Let me repeat that: YOU CANNOT LOSE WITH A 3K+ STACK. No matter what anyone else has. Obviously you can win with less, but you will have to work proportionally harder to do so. Once you have a safe stack, then you bully people on the bubble.
So in a nutshell, in DONs you should seek good spots in position to chip up without overextending yourself with mediocre hands when someone plays back at you. Then abuse the bubble if you have a safe stack, else avoid bubble confrontations against big stacks. Also a good rule of thumb if you're a short stack on the bubble and the big stack is stealing everyone blind. LET THEM! The big stack getting bigger in a DON doesn't hurt you. You're not trying to beat him, you're trying to beat just one other player. So don't feel like you have to play back at a big stack's wide range like you would in a SNG where 1st place is in contention, especially as your fold equity dwindles substantially.