5.a3?! - 5.O-O makes alot more sense. Besides being a solid developing move, 5...a6 can be met by 6.Bxc6 dxc6 7.Nxe5, winning a pawn.

6...bxc6? - You want to play 6...dxc6! because now 7.Nxe5 can be met effectively by 7...Bxf2+! 8.Kxf2 Qd4+ and you've not only won back the pawn,  you've also exposed your opponent's king and prevented him from castling. :)

8.Nf3? - White missed 8.d4!, holding onto the extra pawn.

8...Nxe4! - And things are equal again. e-pawn openings can be very sharp... all of these tactical ideas hiding just beneath the surface...

9.d4?? - Oops.

9...Nxc3! - Yeehaw! You have a won game now. :)

26...Bxc1? - Oops again.

Nice technique finishing your opponent off after the blunder.