Wales flanker Williams and international team-mate centre Shanklin are double Grand Slam winners and helped inspire the Blues to the Heineken Cup semi-finals in 2009 and Amlin Cup Challenge trophy in 2010.
Squillaci looked set to clear Youssouf Mulumbu's long ball forward only for Almunia to come needlessly racing off his line, seemingly confuse his team-mate and allow the Nigerian to double his side's lead.