Injury-hit Australia reached the World Cup quarter-finals with a 68-22 win over Russia but they suffered another blow with Drew Mitchell likely to be out for the tournament. In the lop-sided romp, the Wallabies on Saturday scored 10 tries, seven in the first half, as they put the hapless Russians to the sword even though they would not be happy with the way their game panned out. Mitchell had scored two tries before he pulled up lame with a hamstring injury early in the second half, and coach Robbie Deans said the news was not encouraging. "It doesn't look good. It looks like it will end his tournament so that's a misfortune for him and us. "Fortunately we have four backs coming back to us next week so that will alleviate that (injury) problem," Deans said adding they were now waiting clearance to bring out another loose forward for the injured Wycliff Palu. Wallabies captain James Horwill said the positives for Australia against Russia were in the first half. "We started the way we wanted to. We played up-tempo and really worked to keep the ball movement up," he said. "The second half, probably, we didn't get as direct as we wanted to be and we were a little loose in certain areas." Australia must now wait on the outcome of Sunday's match between Ireland and Italy to determine whether they play South Africa or Wales in the quarter-finals. An Ireland win will mean South Africa next. The raft of injuries to the Wallabies meant heavyweight backrower Radike Samo started on one wing against Russia and scrum-half Nick Phipps was called on to replace Mitchell when he went off. But even with the makeshift look there was never any doubt about the outcome, although Australia went off the boil after Horwill, openside flanker David Pocock and hooker Stephen Moore were replaced at half-time. Samo's first touch of the ball led to Australia's first try when he used his bulk on a 30-metre rampage down the right side of the field, taking play inside the Russian 22. Luke Burgess switched play to the left and Berrick Barnes strolled through the scattered Russian defence to open the scoring. O'Connor missed the conversion but was spot on for the rest of the half as Drew Mitchell, Ben McCalman, David Pocock twice, Stephen Moore and Adam Ashley-Cooper scored to put them 47-5 up at the break. When they led 33-0 after 20 minutes their World Cup record of 142-0 over Namibia in 2003 appeared under threat, but Russia had other ideas. Their first try on the half-hour mark came when Wallabies halfback Burgess latched on to turnover ball and appeared to have run Australia out of trouble with a 40-metre dash upfield before he slipped and lost possession. With most of the Wallabies up in support, Russian wing Vladimir Ostroushko had only lagging lock Nathan Sharpe to beat as he raced nearly half the length of the field to score. The Wallabies were on the board immediately the second half started with a try by replacement prop Salesi Ma'afu. Konstantin Rachkov replied with a drop goal for Russia and Drew Mitchell immediately came back for Australia with his second try. But from there the Wallabies lost their cohesion and to the delight of the crowd who firmly supported the underdogs, Denis Simplikevich intercepted a wayward Quade Cooper pass to score. Konstantin Rachkov landed the conversion and then scored himself before Barnes ended the match with his second try.