Top pair meh kicker on monotone board on the bubble

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$100 buy-in tourney with ~90 entrants down to 21. Top 20 pay and get their buy-in back. AKA the bubble.

My stack is ~11,000 and the button has ~16,000. Blinds are 300/600 with a small ante. I have not paid close attention to the table, but play overall has been bad. I have played very straight forward.

Ok, I get dealt A9 [img]/images/graemlins/spade.gif[/img] in the BB. It was folded to the button who raises to 1500. SB folds and I call the 900. Flop is A75 [img]/images/graemlins/diamond.gif[/img]s.

I check and he bets 500, I call. Turn is 9 [img]/images/graemlins/heart.gif[/img]. I check again and he bets 500, I call. River is a 2 [img]/images/graemlins/club.gif[/img]. so final board is (A [img]/images/graemlins/diamond.gif[/img]7 [img]/images/graemlins/diamond.gif[/img]5 [img]/images/graemlins/diamond.gif[/img])(9 [img]/images/graemlins/heart.gif[/img])(2 [img]/images/graemlins/club.gif[/img]). I check again on the river hoping to induce a bluff. He quickly fires 5,000. WTF??? All comments welcome and appreciated.