Leading any list of Australian Open title contenders are the top three seeds in the men’s draw and the top four seeds in the women’s draw.  All seven of them remain in the tournament through the first four rounds, which suggests that the Australian Open could feature semifinal lineups of top-four seeds in both singles draws for the first time in the tournament’s history.  We catch up with how each of them has fared so far while preparing you for their final tests before those marquee collisions that already have made fans salivate.

Djokovic:  Through the first three rounds, the defending champion looked his normal untouchable self on these courts where he has played his best tennis.  Djokovic toyed with opponents young (Ryan Harrison) and old (Radek Stepanek) while showcasing the fluid transition game that the Australian Open surface showcases more than any other major.  Then came the five-hour war of attrition against Wawrinka, not an opponent expected to detain him for long in view of his ten-match losing streak to the Serb.  Clearly outplayed for long stretches of that match, Djokovic came within five points of defeat and can thank an Enric Molina overrule for preventing the underdog from serving for the match.  If he can recover successfully, as he did last year, his pre-final route still looks smooth.  Quarterfinal opponent Berdych has the game to upset anyone and will arrive fresh, not having lost a set, but he remains winless in ten hard-court meetings with Djokovic

Federer:  He may have entered the tournament as the second-favorite for the title behind Djokovic, but he plowed through the most formidable draw of any contender without losing a set.  In fact, Federer has not lost his serve in the tournament, although indifferent returning by some of his opponents may have contributed to that streak.  Even weaknesses like his backhand and movement have looked smooth and silky so far, while he has found his best tennis at the few pivotal moments in his matches.  Among the few matters of concern is his low conversion rate on break points, even against modest servers like Davydenko.  Federer will want to improve that percentage before he reaches Murray in the semifinals, two days after a clash with Tsonga.  Having defeated the Frenchman easily in the second week of Melbourne before, he will feel confident of blunting his raw power through variety again, although this shot-maker’s explosiveness makes him dangerous at any time.

Murray:  Not dropping a set en route to the quarterfinals, he benefited from an accommodating draw that featured no opponent more notable than Gilles Simon, the sort of counterpuncher who cannot harm the Scot.  Murray looked uncomfortable with his timing in many of these matches, though, and especially in his service games.  With Federer holding serve so regularly, he cannot afford to donate many service breaks of his own when he faces the Swiss.  Before then, Murray should find the challenge posed by Jeremy Chardy much less formidable.  While Chardy upset Del Potro in a five-setter, his uneven form and unreliable backhand play into the hands of an opponent as versatile and steady as Murray.  And, although his timing struggles have frustrated him, the US Open champion looks more composed than at some previous majors.

Azarenka:  Like fellow defending champion Djokovic, she has struggled a bit more than she did at this tournament last year.  Her main test came in the third round, when she dropped a set and several service games to unheralded American Jamie Hampton.  Fortunate that a back injury hampered her challenger in the final set, Azarenka must address those problems on serve to halt her current losing streak against Serena if the two meet in the semifinals as expected.  Her other three matches unfolded less eventfully, however, including a double-breadstick victory over Elena Vesnina that set her back on track in the fourth round after the Hampton wobble.  And Azarenka should stay steady enough to get past two-time major champion Svetlana Kuznetsova in the quarterfinals, for the latter remains too inconsistent despite her recent surge.

Sharapova:  She set a record at this tournament for the fewest games ever lost by any player through four matches at the Australian Open:  five.  Yes, five.  That number should tell you all that you need to know about Sharapova’s dominance here, when opponents have struggled simply to win points from the relentless Russian who has reached three finals in Melbourne.  Among her victims was the admittedly fading Venus Williams, who proved an ideal foil to showcase the world #2’s breathtaking return of serve and seemingly improved movement.  Sharapova has won all four of her matches against quarterfinal opponent Ekaterina Makarova, and she typically devours fellow Russians—with a few notable exceptions at majors.  One of her victories over Makarova came in the same round here last year, a straight-setter that the underdog has vowed to avenge.  Easier said than done, one suspects.

Serena:  Conceding only three games more than Sharapova through four rounds, Serena similarly has feasted on a thoroughly overmatched group of challengers.  Also like Sharapova, she has lost serve only once in the tournament.  Serena looks determined to improve on her fourth-round exit from Melbourne last year, and she stands within range of her longest winning streak to date.  (In fact, she has lost only one match since Roland Garros.)  While first-time major quarterfinalist Sloane Stephens has shown plenty of promise for the future, Serena should dispatch her young compatriot without trouble en route to another collision with world #1 Azarenka at a marquee tournament.  As long as she continues to throttle opponents with her serve, they cannot catch their breath to match her hold for hold.

Radwanska:  Undefeated through thirteen matches this year, the Pole has not even dropped a set yet continues to fly under the radar because she remains unproven as a major champion.  Mats Wilander rightly said that no player can become a favorite to win a major until they win their first, and probably no woman in the draw other than Serena can become the favorite as long as she remains in Melbourne.  That said, Radwanska has fused her deft game with an enhanced serve at an extremely high level of execution since a shaky start to her first match.  Often struggling for confidence, she looks stronger in that regard than ever before, although she has not faced any meaningful competition.  The last part will change in a quarterfinal against Li Na, who defeated her three times last year before Radwanska reversed that trend in Sydney last week.  Most would conclude that the Pole faces the stiffest competition of any top-four seed.