The Rogers Cup, the first of back-to-back Masters Series tournaments prior to the Olympics, began yesterday in Toronto. The Canadian tennis event and the Western & Southern Financial Group Masters next week in Cincinnati, both hard-court tournaments featuring all the big guns, could help settle who is really numero uno as well as provide a preview for the U.S. Open in late August. Questions, questions. Can struggling world No. 1 Roger Federer extend his 234-week reign at the top of the game or will surging Rafael Nadal supplant the Swiss Maestro with a torrid summer? The No. 2-ranked Spaniard certainly has momentum in his corner after blitzing Federer in the French Open final and then following that up with an epic five-set victory over the five-time defending champion at Wimbledon a month later. Also in the mix, at least for bragging rights if not the points race, is Novak Djokovic, last year’s Rogers Cup champion. The No. 3-ranked Serbian is arguably the best hard-court player in the game, with titles at the Australian Open and Indian Wells earlier this year. Federer has been shut out of the first three grand slam tournaments for the first time since 2002 and desperately wants to regain his dominance prior to the U.S, Open. Nadal, who pulled out of a clay-court tournament with a knee injury the week following Wimbledon, must prove his knees can withstand the rigors of the summer hard-court season. After winning the same tournament in Stuttgart last July, Nadal, plagued off and on with knee tendinitis, went without a title until April of this year when he won Monte Carlo. Included in that drought were straight-set, one-sided losses to Jo-Wilfried Tsonga in the semis at Melbourne, Djokovic in the final at Indian Wells, and Nikolay Davydenko in the final at Miami. The common factor in the defeats: all were on hard courts. In fact, just five of Nadal’s 29 career titles have been on hard courts. So the Mallorcan has something to prove. The effort is always there, no question, but the knees don’t always seem to hold up to all the pounding on unforgiving surfaces. I look for Djokovic to emerge as the dominant player this summer, even if he can’t garner enough points to supplant either of his rivals in the rankings. He really has very little pressure on him. All the interest and scrutiny is focused on the rivalry between Federer and Nadal and their duel for No. 1. Djokovic has defeated Federer two of the last three times they’ve met on hard courts and has posted a 3-2 record against Nadal on surfaces other than clay or grass. Serve ’em up.