Cape Town - Proteas Test captain Graeme Smith says they must be more ruthless after they let a golden opportunity to beat Australia slip by.WIN Beer for a YearWIN a Toshiba Touch Screen TabletSouth Africa last won a Test series on home soil in December 2008 against Bangladesh. They lost to Australia in early 2009, drew with England in 2010, drew with India at the beginning of this year and also drew the recent two-Test series 1-1 against the Aussies.The Proteas looked set to win a home Test series against Australia for the first time since 1970 before the Aussies successfully chased down a 310-run winning target in the final Test at the Wanderers for a record fourth innings chase at the ground.And captain Smith acknowledges that they need to be more focused for the duration of a series."One of the things that we need to cut out is our proneness to follow up a good session with a bad one and we also need to be more ruthless when we find ourselves in a winning position," Smith told the Rapport newspaper. However, despite their inability to claim a series win, the captain insists they can take a lot out of the drawn series."The Test series against Australia wasn't a disappointment, especially because we played few big cricket in the eight months prior to that," said Smith.The Proteas start a three-Test series against Sri Lanka at SuperSport Park in Centurion on December 15.