Roger Federer has finally played his trump card in the battle to overhaul Rafael Nadal, luring revered Australian coach Darren Cahill to Dubai for trial sessions. Federer's agent, Tony Godsick, yesterday confirmed Cahill was working with the Swiss right-hander in the Middle East before U.S. hardcourt and European claycourt events. Cahill, 43, looks sure to take a more permanent role with world No.2 Federer after his resignation last month as Australia's Davis Cup coach because of personal and business reasons. Cahill's probable involvement with Federer was first raised by the The Advertiser on February 20. Cahill has known Federer, 27, for 14 years. The pair often have been linked as the perfect coach-player combination. Now that seems to be a reality. For five seasons, from 2003 to 2007, Federer was unrivalled as the greatest player in the world, snaring the bulk of his 13 major crowns. Over a similar period, Cahill had taken Lleyton Hewitt, as the youngest season-ending world No.1, and Andre Agassi, the oldest to regain the No.1 mantle, to the top of the sport. Godsick's confirmation of the Cahill and Federer partnership burned around the tennis telegraph, breathing fresh life into the Swiss master's attempt to dethrone dominant Spaniard Nadal. "Yes, the two (Federer and Cahill) have met in Dubai and played a few balls together," Godsick, of International Management Group, said. "It is a test for both. One cannot yet say whether it will be something long-term. They work together now and see how it works out. "The two have long had a great respect for each other. It was occasionally discussed. It's a trial. Now that Roger's had a break, anyway, because of his back, the timing was perfect for a test. So Roger's with him and has reported that he's arrived." Cahill would become Federer's third Australian coach after Peter Carter and Sydney's Tony Roche. Cahill first watched Federer play in Basle in 1995 when Carter, tragically killed in a South African car accident in 2002, was the future star's formative coach. "No question, he looked good," Cahill wrote in January, 2007. "The kid had a fast arm with a strong forehand and a good feel for the ball. He was far from perfect and, to be honest, I thought there was a kid back in Adelaide (Hewitt) who was potentially better."