LONDON. Top seed Novak Djokovic reached the semi-finals at Wimbledon for the fourth year in a row with a comfortable defeat of the Czech Republic’s Tomas Berdych. Djokovic, who has yet to drop a set in the tournament, won 7-6 (7-5) 6-4 6-3.Berdych, runner-up in 2010, broke twice in the second set to lead 3-0 but made too many mistakes at pivotal moments.Former champion Djokovic will play Argentina’s Juan Martin del Potro, who beat David Ferrer in straight sets, for a place in the final.The Argentine recovered from a nasty fall in the first game of the match to advance to the last four and said he would "do my best” to be ready for the Djokovic match on Friday."I have experience with injuries. I know it’s the semi-finals of a Grand Slam. All the players feel something, some pains, it’s normal,” said the eighth seed.Britain’s second seed Andy Murray, who overcame Fernando Verdasco in a five-set thriller, is in the other side of the draw and will face Jerzy Janowicz for a place in the final.Djokovic warned the rest of those contending for the title that he was playing as well as he ever has at the All England Club.Seventh seed Berdych trailed Djokovic 13-2 in head-to-head encounters before the match but beat his rival at Wimbledon in 2010, in their only previous meeting on grass.Djokovic, winner of the men’s singles at Wimbledon in 2011 and bidding for his seventh major title, has now reached 13 consecutive semi-finals at Grand Slam tournaments.Eighth seed Del Potro looked like he might not last a game of his last-eight encounter against fourth seed Ferrer. The 24-year-old Del Potro prevailed 6-2 6-4 7-6 (7-5) in two hours and 16 minutes to reach his first Wimbledon semi-final.