Djokovic through to semi-finals at year-ender

By Martyn Herman LONDON (Reuters) - Serbia's Novak Djokovic clinched his place in the semi-finals of the ATP World Tour Finals when he beat Tomas Berdych 6-3 7-5 in his last round-robin match on Thursday. The world number one required one set to guarantee the runners-up spot in the Stan Smith Group behind unbeaten section winner Roger Federer who earlier beat Kei Nishikori. Djokovic will face Rafael Nadal in the last four on Saturday with six-times champion Federer up against either Stanislas Wa