Tennis-Serena faces tricky ascent to seventh heaven

By Greg Stutchbury MELBOURNE, Jan 15 (Reuters) - Ailing knees, Father Time and even a resurgent Victoria Azarenka stand in the way of Serena Williams clinching her seventh Australian Open title and giving her one more shot at an achievement that would cap her storied career. Williams, already considered one of the all time greats, has 21 grand slam singles titles, four Olympic gold medals and more than $74 million in career earnings but the 34-year-old is no doubt aiming to become the greatest of them all. She had the opportunity last year to clinch the only feat missing from her resume and become the first female player since Steffi Graf in 1988 to capture a calendar grand slam at the U.S. Open. Victory at Flushing Meadows would have moved her into a tie with Graf on 22 grand slam titles, the most in the Open era, and two behind the all-time leader, Australia's Margaret Court. Instead, knees that were constantly causing her pain and a sore elbow that reduced the power on her serve and groundstrokes, ended her hopes in the semi-finals. She skipped the remainder of the year to recuperate, also indicating the mental pressure to achieve the grand slam had taken a toll as she admitted her heart had been broken by the defeat to Italy's Roberta Vinci. The rest, no doubt helped her refresh physically and mentally, but of greater concern is her propensity to self-destruct -- as she previously has done in Melbourne -- and the continued issues with her knees. Coach Patrick Mouratoglou said last year she had 'very little' cartilage left in the joints and she was forced out of the Hopman Cup in Perth last week with more knee pain. AZARENKA THREAT Williams described that withdrawal as merely 'a hiccup' as she completed her preparations for the season-opening grand slam under Mouratoglou's gaze at Melbourne Park. The Frenchman was also no doubt casting a glance towards the resurgence of Azarenka, who has had a tormented two years with foot injuries and a downward spiral in the rankings. The Belarusian, who won successive Australian Opens in 2012 and 2013, however, stormed to victory in Brisbane last week as she dropped just 17 games over five matches to claim her first title since the Cincinnati Masters in August 2013. She is one of the few players with the power and speed to consistently challenge world number one Williams, who she pushed to a deciding set in each of their three matches last year while ostensibly still on the comeback trail. The 26-year-old is drawn to meet third seed Garbine Muguruza in the fourth round, with the 22-year-old Spaniard also tipped to contend after she made her first grand slam final last year, losing to Williams at Wimbledon. The aggressive, power-hitting Muguruza heads the swag of young pretenders looking to finally usurp Williams, with second seed Simona Halep and fourth seed Agnieszka Radwanska also in contention. The biggest issue the Romanian and Pole face, however, is they both rely on court craft and a touch game to succeed with neither able to pull out a massive serve or blistering groundstroke to blast a winner when it is needed. Two veterans who do have those attributes are multiple grand slam winners Maria Sharapova and Serena's older sister Venus, though the Russian has an arm injury and is drawn to face the world number one in the quarter-finals. Venus, who is on course to face Halep in the quarter-finals, despite winning three titles last year and ending inside the top-10 for the first time since 2010, has also only advanced to the last eight in Melbourne three times since 2003. (Editing by John O'Brien)