Rich seam: In Sean McMahon, the Wallabies have a player with some ‘dog’ Warren Gatland has gone for his own double openside lineup, with Justin Tipuric in for the injured Dan Lydiate.McMahon has the opportunity to announce himself on the global stage, even he will probably only have one game to show what he can do before Hooper returns for the quarter-finals. Like Georgian props, Springbok locks and Fijian wingers, Australia seem to have a conveyor belt of talent at openside with no end in sight.England felt the full force of Michael Cheika’s dual-openside tactic in defeat at Twickenham last Saturday, and while Michael Hooper’s suspension means Wales will avoid ‘Pooper’, the tactic hasn’t been abandoned.Rather than shifting David Pocock back into the seven jersey, Cheika has given youngster Sean McMahon a second start of the tournament, filling in for Hooper.Michael Hooper and David Pocock will be split up this week. Photo: Getty Images.He’s certainly doesn’t have the vice captain’s experience, and is a slightly different sort of player, but the 21-year-old Melbourne Rebel could prove a real handful for Wales.Preferred to the supremely gifted Liam Gill and Wallaby legend and Wasps flanker George Smith, McMahon was a surprise inclusion in the Australian squad, having not featured at all in the Rugby Championship.His only previous Test experience came during Australia’s unsuccessful autumn tour last season, starting three games: the inevitable close win over Wales as well as the defeats to France and England. A year on, and McMahon has clearly grown as a player, and while his international matches in 2015 have come against the USA and Uruguay, he has looked a much improved player.More physically imposing than Hooper, he will certainly offer a carrying threat that some critics believe is lacking from the Australian back row.While he reportedly weighs 100kg, similar to Hooper and some 15kg lighter than Pocock, McMahon carries with even greater conviction, and will take some stopping.Michael Cheika has made a bold call to start McMahon. Photo: Getty Images.Last summer he was still playing age group rugby for the Wallabies, but his physicality has impressed in training and Cheika had no qualms over chucking him straight in for this encounter. LATEST RUGBY WORLD MAGAZINE SUBSCRIPTION DEALS Australia have taken a gamble by starting Sean McMahon against Wales but the young openside has bags of potential.