BANGALORE (Reuters) Kevin O’Brien smashed the fastest ever World Cup century to propel Ireland to a stunning three-wicket win over England in a Group B match on Wednesday.An astonishing knock by O’Brien, who clobbered 13 fours and six sixes to reach three figures in only 50 balls, helped the Irish to live up to their reputation as giant-killers as they overhauled England’s total of 327-8 with five balls to spare. It was the highest successful run chase in the tournament.Four years after beating Pakistan in the group stage in the Caribbean, the Irish repeated the feat to dent England’s hopes of progressing into the knockout stages of the 2011 tournament.O’Brien was eventually run out for 113 but his team mates made sure his effort had not been in vain.