My great Day 1 fold

I totally forgot to put probably the most crucial hand of the day into my summary.

At the 200/400 level with 50 ante, I had around 46k. I raised under the gun with AK off to 1100. I received 5 calls. With the pot now at around 5600, the flop was Ac 6c 2s. I led out with 3600. I received a call from the player behind me. The next player to act made to 10,500. The other two players folded. At this point, I had a decision. This player had around the same stack as me with about 40k. I figured in my head that the odds he raised with a flush draw here are between 5-1%. He seemed to be one of the more intelligent players at the table. I basically just had to put him on a hand and then make a big decision. Just calling here was not an option because any flush draw can't get a free card here, especially considering the guy behind me was the most likely guy on a flush draw. Furthermore, the guy behind could also be slowplaying a set even though I ruled this out after some thought. Not many players are willing to let 3 players behind them in the pot with a set when an obvious flush draw is on board. I relayed this logic right over to the player who I believed was a good player and thought about how I would play the hand. Would I be raising here with a worse ace? Pretty much never. Would I be raising here with AK, probably not often. Would AK be a possibility for this guy? Judging by the amount of 3 betting he had done, I don't see a flat call with AK as being a big possibility. He has to have a set. He knows I've played pretty good so far. He knows I raised under the gun meaning I have a strong hand. For him to make that raise in this situation, I just have to be beat. I folded my hand. The other player called. The turn was a K of spades. The first player checked, the on the flop raiser moved all in for like 30k. The other guy called. The raiser showed 66 for a set and the other player had K 10 of clubs for the nut flush draw. I got up from the table and pumped my fist as I know that this type of hand could have easily knocked me out of the tournament.