Burton underlined their promotion potential with a 2-0 win over rivals Coventry - ending their unbeaten home league record.The Sky Blues, who had surrendered a lead in midweek against Walsall, were undone by fine margins again.After creating the best of the first-half chances but again failing to convert them into something tangible, they gifted Calum Butcher a 49th-minute goal.Young full-back Aaron Phillips tried to chest a long ball back to his keeper but only diverted into Butcher's path and he made no mistake.Albion, who looked solid all over the pitch, could easily have stretched their advantage before Stuart Beavon earned his deserved goal in the 72nd minute.Burton keeper Jon McLaughlin had kept his side on level terms in the first half when he twice denied teenager James Maddison but had little to do after the break.Beavon's 73rd-minute goal sealed their victory. Coventry were caught over-playing deep in their own half and when Peter Ramage failed to deal with a high ball, the striker struck.