MADRID (AFP) - Untouchable 27-0 Novak Djokovic admitted Tuesday he's living a tennis dream which cannot go on. The second seed at the ATP-WTA Madrid Masters has not been beaten at all in 2011 and owns five titles coming into his first serious clay test of the spring as the French Open start on May 22 draws near. "I don't think it's realistic to go without a defeat in the first for months of the season," admitted the Serb as he prepared to face an opening match against South African Kevin Anderson, a winner over Olivier Rochus in the first round 6-2, 6-4. "But anything is possible if you believe you can achieve it and you are fit physically and mentally fresh, motivated and dedicated to the sport," said the world number two behind Rafael Nadal. "I've been working very hard on my game, my mental approach over the past few years and now it's paying off. There is no secret." Djokovic, who latest trophy triumph came at his family-owned Serbian Open on Sunday, added: "I always knew I had the quality, I just needed to get things together - and that's happening right now." But Djokovic does not believe his dream can go on forever. "I don't believe I can win every match on clay, but I'll take it one match at a time and we'll see how far it can go." While Djokovic, who played Madrid in 2009 with a marathon semi-final loss to Rafael Nadal and withdrew last year with illness, was psyching up for battle, Estoril champion Juan Del Potro was reaching the second round, defeating 13th seed Mikhail Youzhny 6-1, 3-6, 6-3. Del Potro, the 2009 US Open champion, missed more than eight months of play last season after wrist surgery but has now won two titles in 2011. He has claimed victories in 24 or 28 matches since February as his return towards the elite gains pace. German Florian Mayer eliminated 16th-seeded Serb Viktor Troicki 4-6, 7-5, 6-4 while Frenchman Gilles Simon booked a second-round spot against fourth seeded Andy Murray through a win over Ivan Ljubicic 7-5, 7-6 (10/9). Three women's seeds reached the third round, with number one Caroline Wozniacki leading the way as she held off Serbia's Bojana Jovanovski 6-4, 6-4. Australian Samantha Stosur defeated Daniela Hantuchova for the second time in a fortnight on red clay, winning 7-6 (7/1), 7-5 winner in a match which was almost interrupted by a huge thunderclap in the skies over the Caja Magica. The noise caught Hantuchova off-guard, with the flinching Slovak asking to stop play. But with Stosur closing in on victory, the match went ahead, with the French Open finalist advancing on her second match point in just under two hours of play moments later. Stosur lifted her clay record in 2011 to 6-2 as she closes in on her career-best in Madrid, a quarter-final last year. "It was a tough match and I'm glad to get through. I was ready to play a third set if it had gone to that. I just tried to stay in the moment and play each point as it came," said Stosur. Czech 16th seed Petra Kvitova also advanced 6-3, 6-3 past South African Chanelle Scheepers as Bethanie Mattek-Sands hammered fellow King 6-0, 6-2.