BEIJING, Jan. 24 (Xinhuanet) -- Roger Federer and Andre Agassi set-up a quarter-final showdown between the current and former world number ones after they both emerged victorious at the Australian Open on Sunday.

 
   Federer kept his Australian Open title defense on track with a commanding 6-2, 6-2, 7-6 fourth-round win over talented Cypriot qualifier Marcos Baghdatis.

   Agassi, a four-time champion in Melbourne, The 34-year-old Agassi, seeking a fifth Australian title, stayed on course for a possible fifth title with a 6-7, 7-6, 7-6, 6-4 win over big-serving Swede Joachim Johansson when he was asked about Federer

     "Who's Roger?" he joked.

     Here, they don’t always know what to say first when announcing his entrance: world No 1, top seed or defending champion. They usually swap them around for variety’s sake. Federer limits himself to a brief flutter of his hand whereas when Agassi pitter-patters into view, he accords the public several swishes of his racket. For a long time during his two hour, 38 minute fourth-round match against Joachim Johansson yesterday, that was all he was able to do as the American attempted to withstand a barrage of aces from the 6ft 6in boy mountain from Lund, in Sweden.

 
    Another mouth-watering contest is looming in the women's draw after Wimbledon champion Maria Sharapova advanced to the quarter-finals against her fellow Russian and U.S. Open holder Svetlana Kuznetsova.

    Sharapova recovered from trailing by a set and a break in the second to overcome Italian Silvia Farina Elia, 4-6, 6-1, 6-2, while Kuznetsova overpowered her compatriot Vera Douchevina, 6-4, 6-2.

 
    Serena Williams, who completed a non-calendar year grand slam when she won in Melbourne two years ago, was forced to dig deep before beating 11th-seeded Russian Nadia Petrova, 6-1, 3-6, 6-3.

    The American will play second seeded Frenchwoman Amelie Mauresmo, a 6-2, 6-4 winner over Russia's Evgenia Linetskaya, but said she had a lot of work to do.

    "To be honest, I didn't deserve to win the way I played," Williams growled.

    "My serve was horrible. I made errors. I didn't play well or hit my shots right. I'm going to have to improve a lot in my next match or it's going to be a struggle."