'No limits' for Serena in her chase for greatness

    (CNN)It's a verdict which will send shivers down the spines of the world's top female tennis players -- Serena Williams has been tipped to continue her domination at the very top for years to come.

    That's the view of her coach Patrick Mouratoglou who says Williams is well set to surpass Steffi Graf's Open Era record of 22 grand slam singles titles.
    The 33-year-old will go into the French Open, which starts Sunday, aiming to secure a third title on the clay courts of Roland Garros and the 20th grand slam success of her career.
      "How many can she win? I don't want to give her a limit," Mouratoglou told CNN.
      "Since she wants to keep on playing and winning, she can do it. I think she's still the world No. 1.
      "She's still winning grand slams, she won the Australian Open a few months ago. Why not keep on winning?"
      Williams has suffered just one defeat in 2015 and while she was forced to pull out of the Italian Open with an elbow problem, there are few who would bet against her in Paris.
      Mouratoglou, who previously worked with Grigor Dimitrov, arrived on the scene after Williams had crashed out in the first round at Roland Garros three years ago.
      It was the only time Williams had lost in the opening round of a grand slam and led to questions over her ability to remain at the top of women's tennis.
      Injury and illness also played its part in her frustrations as her ranking sunk to 175th in the world.
      Her comeback is well documented -- the whispers of her demise silenced in emphatic style.
      In 2013 she won 11 titles -- including the U.S. Open, French Open and the end-of-season WTA Championships -- the best record in the women's game since Martina Hingis in 1997.
      Last year was a rather more difficult affair -- her victory at the U.S. Open her only success at a grand slam.
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      Williams, who arrived in Paris 12 months ago as the defending champion, was stunned by Spain's Garbiñe Muguruza in the second round.
      It was not just the defeat which shocked the world of tennis but also the nature of it.
      Williams, the world No. 1, was beaten 6-2 6-2 in just over an hour in a contest where she made 29 unforced errors.
      She also won fewer games than in any of her 288 previous grand slam matches.
      Such a performance led to her conqueror, Muguruza, telling reporters that "the new generation [has to] come through and I think now is the moment."
      That bold prediction quickly fell flat in terms of Williams having her power curtailed.
      True she exited Wimbledon and suffered a viral illness which forced her to withdraw from the doubles tournament with her sister, Venus, but Serena quickly returned to form by winning the U.S. Open.
      Then in January she took her tally of grand slams to 19 by winning in Melbourne.
      Her victory over world No. 2 Maria Sharapova was the 16th time in succession she had beaten the Russian.
      "I think she can improve a lot," said Mouratoglou. "It's incredible to say that when you look at how good she is and all the achievements she's made for so many years.
      "Everybody can improve -- even the world No. 1 can improve and she can."
      Williams turns 34 in September, but Mouratoglou has tasked the American with improving her volleying.
      "I think her game at the net for sure can improve and the transition from the baseline to the net can be improved a lot," he said.
      "Her swing volley can be better, sometimes she's hesitating to move forward and she plays one more shot when she could come up and finish it with a swing volley."
      If there is work to be done on her volleying, Mouratoglou pinpointed her serve and tactical nous as the bedrock of her game.
      "There are a lot of areas but of course she's the best server, she's the most powerful player, she probably has the strongest ground strokes on both sides.
      "People see her as a powerful player which is true, but she understands the game really well."
      Serena's grand slam triumphs

      Serena's grand slam triumphs

      Australian Open 6

      2003, 2005, 2007, 2009, 2010, 2015

      French Open 2

      2002, 2013

      Wimbledon 5

      2002, 2003, 2009, 2010, 2012

      US Open 6

      1999, 2002, 2008, 2012, 2013, 2014

      More than a decade separate Williams' triumphs at Roland Garros -- her first victory coming in 2002.
      This year she will face her foes once again with Romania's Simona Halep hoping to improve on last year's runners-up spot.
      Halep's progress has not gone unnoticed -- the world No. 3 has impressed Mouratoglou over the past year with the Frenchman extolling the virtues of her movement on the court.
      The likes of Halep and American Madison Keys are two players who Mouratoglou has picked out to become stars in the coming years -- but they may have to wait their turn.
      He remains determined to ensure Williams dominates while her body remains able to withstand the rigor at the very top.
      Not that she requires much persuasion.
      "I don't do so much to motivate her -- she's unbelievable," he says while laughing.
      "She's just a champion and I think the difference between champions and other players is this ability to always look in front of them -- they never look behind."
      Williams' opponents may not be so fortunate -- they might be looking over their shoulder for a little while longer yet.