Herman MostertCape Town - The Blitzbokke have defeated Canada in the semi-finals of the Plate competition at the Wellington leg of the HSBC Sevens World Series.South Africa won 21-19, after leading 14-7 at half-time.Canada started well, earning two early penalties that gave them the go-forward momentum to launch an attack into the South African half. They spread the ball well across the field and Taylor Paris sprinted brilliantly to score in the corner after two minutes.Nathan Hirayama kicked the tough conversion to put Canada 7-0 up.But the South Africans were quick to hit back and levelled matters two minutes later when speedster Cornal Hendricks went over under the posts. Cecil Afrika converted to level the scores.Captain Kyle Brown then scored straight from the ensuing restart. Afrika converted for a 14-7 advantage with 10 seconds remaining in the first period.Canada failed to catch the restart and South Africa looked like adding another try when Hendricks made a brilliant break but they failed to control the ball in front of the Canadian line and went into half-time seven points up.Canada hit back early in the second half when Paris scored his second try after following up a chip kick. Hirayama converted to level matters (14-all).But South Africa's response was swift and Sevens new-boy Stephan Dippenaar scored under the posts from the ensuing kick-off.Afrika converted for a 21-14 lead.However, the Canadians refused to lie down and hit back when Ciaran Hearn scored in the corner with time running out. Hirayama hit the posts with his conversion attempt to leave South Africa 21-19 ahead.South Africa failed to control the ensuing kick-off, which gave Canada a scrum right in the middle of the park in an attacking position with 10 seconds remaining. However, the Boks' defence held out to claim a narrow victory.Earlier, the Blitzbokke lost their Cup quarter-final match 21-5 against Fiji which demoted them to the Plate competition.Canada lost their Cup quarter-final in extra-time when Lolo Lui kicked a penalty for Samoa.South Africa will now play Tonga in the Plate final after the Islanders defeated France 15-7 in their semi-final.