Ghana coach demands an improved performance from his players for the Africa Cup of Nations quarter-final against Cape Verde as the Black Stars bid to reach the last four.The Black Stars, four-time champions will be up against the Blue Sharks in Saturday's clash in Port Elizabeth.Cape Verde, making their tournament debut, defied pre-tournament expectation to sail into the quarter-finals while the competition has bid goodbyes to the likes of defending champions, Zambia, Morocco, Tunisia and Algeria.“I have drawn their [players] attention to the fact that Cape Verde can be a threat and it is important that they all focus on them and take each game as it comes,” the Ghana coach, Kwesi Appiah said on Thursday in Port Elizabeth.Ghana clinched first place in Group B but Appiah expects his players to put in more intensity and go the extra mile to secure a semi-final place.The Black Stars after their opening 2-2 draw against DR Congo, beat Mali 1-0 and finished off the group campaign with a 3-0 victory against Niger.“We need to do extra work and the players need to fight more than what they’ve done already,” he said.The two sides last met in a friendly in November 2012, when a goal from Mubarak Wakaso handed Ghana a 1-0 win in Portugal.However, things have changed since that day with the Blue Sharks showing much improvement.“I have always said that even though we won 1-0 in Portugal in a friendly game and looking at the games they’ve played so far, I totally believe they are a strong side and it’s not going to be easy,” Appiah said.