To be honest many of us in the UK were shocked when Thompson stopped Price! With hindsight though Price was stepped up far too early. He went from domestic level to world level skipping out any European heavies, so he took a risk and it failed. Mares getting stopped was a shock but he was caught cold, it has happened to a lot of fighters over the years.
I don't think anybody predicted Mchunu's shutout of Chambers so that was definitely a big upset. Also I think few predicted how dominant Groves would be against Froch until the dodgy stoppage. For me though the Mares loss was probably the biggest surprise.
Garcia-Matthysse and I don't think its close. Broner hadn't faced nobody and easily got hit in his fights. Maidana is a good pressure fighter with power so the outcome was not surprising but it was the most satisfying.
Mares getting KTFO in the 2nd round by Gonzalez is the biggest upset of the year. Mares had been on a tear and was seen as the future of boxing in the lower weights. No one saw this one coming.