Novak Djokovic Novak Djokovic of Serbia serves in his fourth round match against Nicolas Almagro of Spain during day seven of the 2011 Australian Open at Melbourne Park on January 23, 2011 in Melbourne, Australia.

Berdych vs. Djokovic:    Meeting on two notable occasions in 2010, their encounters spiraled in strikingly divergent directions.  In a Wimbledon semifinal, the Czech fired the first salvo with a comprehensive performance that cruelly contrasted his newfound confidence with the mental foibles that plagued the Serb throughout the first half.  Just a few months later, though,  Djokovic reversed the momentum emphatically with an emotional four-set victory in a Davis Cup semifinal that revealed his revitalized self-belief after his US Open surge while illustrated Berdych’s second-half slump.  With both contestants seemingly rejuvenated, spectators should brace themselves for an encounter more compelling than either of its prequels.

When at his best, the 2008 champion showcases a more complete game than last year’s Wimbledon finalist, who relies more heavily on his forehand despite improving his two-hander.   In addition to his more symmetrical groundstroke arsenal, Djokovic can unleash a lithe movement that trumps his opponent’s ungainly strides, although the surface will allow the Czech a shade more time to arrange limbs that resemble the Pillars of Hercules.   Nevertheless, Berdych has looked impressively poised during his first four rounds, especially when he defused the  volatile shotmakers Gasquet and Verdasco in straight (and straightforward) sets.  Unlikely to ever shed the reputation of mental unreliability, Djokovic slumped in his last two Australian Open quarterfinals after imposing first weeks, so one never knows when another stumble could occur.  The percussive serves of Roddick and Tsonga eventually eroded the Serb’s confidence on those earlier occasions, and Berdych will bring an equally potent weapon to the service notch.  But this surface offers an ideal venue for Djokovic’s ball-redirecting talents and his effortless transitions from defense to offense.

Wawrinka vs. Federer:  While one of these two Swiss players has dropped sets with a casual profligacy, the other has smothered opponents without dropping a set.  Those who didn’t watch the first week almost certainly would cast Federer in the latter role, yet in fact the defending champion has meandered into the quarterfinals in a pedestrian manner.  After a five-set rollercoaster against former nemesis Simon, Roger carelessly tossed a set to Robredo before dispatching the unassuming Spaniard.  Although his serve and net play have remained characteristically crisp, Federer’s groundstrokes have wandered out of his control for extended periods and shone rays of hope onto his opponents.  Quite the contrary, Wawrinka blistered winners from both wings and every corner of the court as he hammered Roddick out of Melbourne.  At the core of that relentless barrage lay a sturdy serve that allowed him to dictate rallies from the outset.  Since Wawrinka regularly threaded the needle with scintillating passing shots, Federer must time his forecourt approaches more judiciously than in his first few rounds.  The Swiss #2’s sole victory over the Swiss #1 came on clay at Monte Carlo, however, in a surface and a setting far from Rod Laver Arena.  Seemingly dulled by a career of subservient status, Wawrinka may not summon the audacity to overthrow his fabled compatriot at one of the calendar’s most prestigious tournaments.  If Federer looks mortal in the early stages, though, his long-time understudy now has the self-belief to exploit his fallibility.

Caroline Wozniacki Caroline Wozniacki of Denmark celebrates a point in her third round match against  Dominika Cibulkova of Slovakia during day five of the 2011 Australian Open at Melbourne Park on January 21, 2011 in Melbourne, Australia.

Wozniacki vs. Schiavone:  As “4:44” joins “70-68” in the lexicon of tennis lore, the 2010 Roland Garros champion has little time to wallow jubilantly in bottles of Barolo.  Like Berdych and Djokovic, Wozniacki and Schiavone collided in two starkly contrasting meetings last year.  En route to the Miracle on Clay, the Italian wove a spiderweb of slices, drop shots, lobs, and looping forehands around the flustered Dane, who revealed not only her ineptitude on clay but her strategic immaturity.  Just as resounding was Wozniacki’s victory at the Rogers Cup early in her outstanding second half; on that occasion, a jaded Schiavone failed to fracture her opponent’s bulletproof baseline.  With the exception of Vania King, the world #1’s adversaries have competed with her on relatively even terms for much of their matches but failed to capitalize upon openings when they emerged.  The ceaselessly alert Schiavone will not hesitate to strike if opportunity knocks, but significant questions hover above her fitness after the longest women’s match at a major.  Most dangerous when she can meticulously construct a rally, the Italian veteran may feel pressed to attempt a risky maneuver too early in a point if she has not fully recovered from her Sunday exertions, which seems likely.  Feasting upon reckless or impatient foes, Wozniacki stands especially well situated to profit from an opponent who scored a historic but Pyrrhic victory. 

Petkovic vs. Li:  A round after halting the ride of the Valkyrie, “Petkorazzi” contests her first Slam quarterfinal against an adversary seeking her second straight Australian Open semifinal.  A physically hampered Venus and a mentally absent Sharapova posed few challenges for the German, who has played just 18 games and 86 minutes of tennis since the second round last Wednesday.  Riding a nine-match winning streak, Li thoroughly dominated world #10 Azarenka with reliable serving and groundstrokes that skidded off the baseline, extracting benign mid-court replies.   A competitor nearly as intense as the Chinese star, Petkovic strikes her groundstrokes with equal conviction while bolstering them with a more formidable serve.  Whereas Li showcases one of the finest two-handed backhands in the WTA, the German has refined one of its more penetrating forehands.   This quarterfinal thus may hinge upon whether cross-court rallies pit forehand against forehand or backhand against backhand; both players strike their weapons extremely early and thus rarely concede the initiative in a rally once seizing it.  Contrasting with Petkovic’s extroverted personality is Li’s understated demeanor, which springs in part from her extensive experience on these momentous stages.  Bearing the scars of many memorable encounters as an underdog against elite contenders, she now has become an elite contender herself with an excellent prospect not only to win this match but perhaps to reach the final.  How will she respond to that status as a first Slam title lies so invitingly within her grasp?