Ross Docherty is challenging his team-mates to rediscover their "winning mentality" as Dundee United eye a Premier Sports Cup semi-final place. United's eight-game unbeaten run ended on Sunday with defeat to Rangers, and captain Docherty wants the side to "right the wrongs" in Friday night's quarter-final against Motherwell. The midfielder, who played his part in last season's Championship-winning side, though he was hampered by injury, came off the bench in the first half against Rangers.