I'm never trusting my brain again

Not only was the 2008 Blayney Open a good tournament to play in, for me it started off with the potential for me to achieve one of my best results ever. Through a combination luck and opening preparation I finished the first day on 3/3. The good opening preparation was in the second round when I played a tricky line against the Caro-Kan and my opponent went down the wrong line. The luck came in round 3 when I played another tricky line, this time in the Four Knights. It turns out that I was simply lost at one point but by opponent (David Castor) chose another plausible, but inferior move and I grabbed the advantage and held on to it for the rest of the game.
As a reward for this I received a fairly 'safe' 4th round pairing and although my opponent had some threats after his opening gambit, swapping off queens put paid to his ambitions and technique did the rest.
So round 5 sees me in the lead alongside top seed Endre Ambrus and although I am aware of the 500+ rating point difference, I figured that I will at least make him work for the point, based on my results so far. Unfortunately for me (and in a sense him) the following occurred. The comments to this game are basically the thoughts going through my head when deciding on my moves.

Press,S - Ambrus,E [B00]
Blayney Open , 07.09.2008
[Press,Shaun]

1.e4 Nc6 Not a surprise, but I'd rather player a double king pawn opening, so I'll try what Emma Guo played earlier in the tournament against him. 2.Nf3 d6 Ok. He didn't play e5, so I'll take my share of the centre. 3.d4 Nf6 4.Nc3 Bg4 5.Be2 e5 Ah, now he plays e5. The obvious move is d5, but after Ne7 followed by Ng6 he starts to build up a kingside attack. Hang on, I might be able to meet this by playing Bg5, followed by d5. The I can look at castling queenside, as well as playing Bxf6 if he moves his knight to e7. 6.Bg5? Bxf3 Damn, I shouldn't have missed this. Now I'm dropping a pawn after Bxf3 Nxd4. What can I do to stop this happening? Ah. If I take on f6 instead he might play Qxf6 when dxe5 saves the pawn. Of course he can simply play gxf6 and he still wins a pawn after Bxf3 Nxd4 but he does have a damaged pawn structure. 7.Bxf6?? Bxe2 (D) Uh oh. I forgot to count the captures. Looks like I'm dropping a piece. No point in trying to fill up the scoresheet with pointless moves so I'll resign here. 0-1

Due to other results I still went into the last round tied for 2nd and my final pairing was against Peter Abbott, who was rated only 2 points more than me. After the 1 move draw on board 1, the winner of our game would take outright second. Having lost miserably in round 5 I at least made more than 7 moves, but I was simply outplayed by Peter and he took 2nd while I had to settle for a share of 7th (and no prize).
In fact my tournament collapse meant I was the only one in the car ride back home without a prize as Endre Ambrus took home 1st prize, while Nick Beare came equal first in the Under 1000 section.