World number one Novak Djokovic has stormed into the semi-finals of the US Open, the fourth and final Grand Slam of the season. The top seeded Serb defeated eighth placed Briton Andy Murray, 7-6, 6-7, 6-2, 6-4. For a place in the finals, Djokovic will meet Kei Nishikori who had stunned third seed Stanislas Wawrinka in the other quarterfinal, 3-6, 7-5, 7-6, 6-7, 6-4 to become the first Japanese in the Open era to reach a Grand Slam semi-final. Ichiya Kumagae was the first Japanese to make it to the semi-final, but that happened in 1918, 50 years before the then-all-amateur tournament became the US Open.In the Women's section, world number one and five-time US Open champion Serena Williams roared into the semi-finals with a 6-3, 6-2 victory over Flavia Pennetta of Italy.Russian Ekaterina Makarova also progressed into the last-4 beating higher seed Victoria Azarenka of Belarus in straight sets, 6-4, 6-2.