Cape Town - England centre Brad Barritt has praised the Springboks' performance against Argentina but at the same time warned them to remain consistent as harder challenges like the All Blacks lie ahead.Barritt, who was born in Durban and represented the Sharks earlier in his career, was speaking to Die Burger earlier this week when his club, Saracens, were in Cape Town as part of their pre-season preparations.He said he was highly impressed with South Africa's 73-13 annihilation of Argentina but challenged to Boks to maintain that level of play."The Springboks were very impressive and clinical. It was a fantastic performance, but in rugby you have to earn respect week after week. They'll need to play even better in order to beat Australia and New Zealand."The All Blacks thumped the Wallabies 47-29 in Sydney last Saturday, but Barritt gave the Boks the top accolade after the first round of the Rugby Championship."The Springboks were the team who dominated the first weekend, but it will be a massive challenge to win in New Zealand."The All Blacks are a team that stay calm and are playing with a lot of confidence."