South African Oscar Pistorius qualified for the semi-finals of the 400m on his historic appearance at the World athletic Championships in Daegu.The first amputee athlete to race in the competition finished third in his heat in 45.39 seconds. The four-time Paralympic champion, 24, finished behind winner Chris Brown, with Britain 's Martyn Rooney second. World and Olympic champion LaShawn Merritt of the United States qualified fastest in 44.35. Pistorius, who has a personal best of 45.07, said he was tired and needed to cool down now to refocus and chat with his coach.