Bears34 was player A, and surprisingly chose W-i4, a connecting opening. Even more surprisingly, Guiduf chose to play as Yellow/Green leaving Bears34 to make the connection. The game had many twists, and a number of questionable moves, but the outcome was that Guiduf won by 19 and advanced. After the game there was a lot of discussion about which move in particular was the biggest error. At one point Bears played a Blue U that Guiduf responded to with a Yellow i5, killing most of the relevant corners on the Blue U. Most players, including Bears34 thought that this was the single biggest error of the game, and was ultimately responsible for the outcome, but I maintained that it was not as bad as it seemed, and that Bears could still play well enough to stay in the tournament, or possibly even win the game at that point, but that more damaging moves came shortly after. To be fair, seeing the Blue U get killed (Guiduffed!) the way it did is definitely tilting, and could certainly have led to compound errors, but strictly in terms of move quality, it was not a tournament-ending blunder.
To that end I have done some analysis using a pentobi file, showing how I think the tournament was still salvageable by Bears34 after the Blue U, and how he could have even won the game if not for a much more damaging error (the Red N). You can access the file here (link : http://dl.dropbox.com/u/27727822/FS2013/bears34-guiduf-freestyle2013.blksgf)
The conclusion I end up drawing is that the Blue U was probably a mistake, but really only about a 3-point mistake. Yellow gained a sizeable zone in the bottom right on account of the Blue U, but also lost tempo, as well as some space in the small DCCZ Red shared with Blue. On the other hand, the Red N two moves later was a big enough mistake to cost the game (and in this case, ultimately the tournament).