Wimbledon: Djokovic keeping calm amid chaos All his rivals may be flapping around like headless chickens, but Novak Djokovic is determined to keep calm and carry on bludgeoning his way through Wimbledon. The cleaners at the All England Club must have had one heck of a job this morning, cleaning up the shredded nails left by Andy Murray fans as they watched the British No 1 come from two sets down to beat Fernando Verdasco and move into the semi-finals. But while the Scot toiled on Centre Court, Djokovic had already finished his day's work. He was at his temporary Wimbledon base, posing for a picture in his golf gear, apparently ready to hit the course for a bit of rest and relaxation. The picture summed up Djokovic's state of mind. Rafael Nadal and Roger Federer are out, Murray is scrapping his way to the last four, and Djokovic is the coolest and calmest man in the whole of SW19. Djokovic has every reason to be feeling like this. He has been in this situation before. Tomorrow's clash against Juan Martin Del Potro will be his fifth Wimbledon semi-final. The Serbian has gone on to win the title once, in 2011, and is drawing on all his experience to keep his nerve. "I'm trying to use that experience that I had in the past, especially in this tournament in 2011, to feel comfortable and calm and confident towards the end of the major tournament," the top seed said. Now I'm in the semi-finals. Hopefully I can go a step further. I'm really going to try to step out on the court in two days and give my best to be in another final of Wimbledon. I believe I can make it. Belief will be key for Djokovic tomorrow because the last time the two met at SW19, it was Del Potro who came out on top. Eleven months ago, the 24-year-old beat the world No 1 in straight sets to win bronze at the Olympics. As that was the only clash between the two on grass, Djokovic is wary of those who already think he is a dead cert to make Sunday's final, where he may play Murray. "He is a quality opponent," Djokovic said of Del Potro, who won the US Open in 2009. There are no real clear favourites now in the later stages of the event, but inspiration is out there, you know. Of course you always want to do your best in the grand slams. Like Djokovic, Del Potro has had a near-perfect progression through Wimbledon so far. The eighth seed has despatched Andreas Seppi, Grega Zemlja, Jesse Levine and fourth seed David Ferrer without losing a set. His only problem has come from his left knee, which he injured against Zemlja last week. The problem resurfaced yesterday when he suffered a nasty fall during his first game against Ferrer. Del Potro took what he described as "magic pills" to get him through the match. The Argentine showed little sign of discomfort today when he practised on Wimbledon's Aorangi courts with his knee in strapping. Del Potro only took up 40 minutes of his allotted hour, prompting fears that he would not be fit for the match, but he thinks he will be fit. "I am okay," he said. I think I will be better for tomorrow. I will think about the match, about Nole (Djokovic) and nothing else. Despite the injury, Del Potro fired down a number of huge forehands yesterday and the win came as a surprise to many given that Ferrer has been playing so well of late that he will definitely move up to third in the world after Wimbledon. The South American believes he can play even better, however. "It will be a difficult day, but I will try to play better than yesterday and try to win," Del Potro added. I am confident at the moment with my serve and all my game. Nole is world number one. Not many can beat him and he is a big favourite for the tournament, but I will try to win.