Unlike in Beijing 2008, Novak Djokovic failed to secure an Olympic medal in London four years later. The Wimbledon champion from a year ago reached the semi-final at the All England Club but lost the crucial encounters to Andy Murray and Juan Martin del Potro in four tight sets to settle with fourth place and miss a medal.Novak lost to Murray 7-5, 7-5 in the semi-final and faced del Potro in a bronze medal match. The Argentine earned a 7-5, 6-4 triumph in an hour and 48 minutes to deliver the first medal for his country in London. Juan Martin defended all six break points and stole Novak’s serve once in each set to emerge at the top and beat the Serb for the second time in a row.The encounter on Court No. 1 started late due to rain, and th …