And so ends the first act of Martina Hingis’s comeback. After accomplishing more at the Australian Open than anyone had expected, the 25-year-old former world no. 1 ran into Kim Clijsters, now a bigger,stronger,quicker version of the scrappy player Hingis used to knock around before she retired in 2002. Clijsters lost four of her first five contests with Hingis and probably did not expect to win in those early days of her career. Tuesday night, as the favorite, she prevailed without her best stuff.

The 22-year-old Belgian scored a ragged 6-3, 2-6, 6-4 victory, prying the world’s no. 1 ranking away from Lindsay Davenport in the process. Her injured hip and back, numbed by painkillers, are holding up. The only question left heading into her semifinal match this morning in Melbourne was whether she would have enough energy in reserve to topple Amelie Mauresmo, whose play has improved considerably as the tournament nears its final weekend.

Clijsters would have done her body a favor had she not lost her rhythm early in the second set. Trailing 6-2, 2-0, Hingis had absorbed a beating, falling so far behind that any hopes she had of winning this quarterfinal had transformed into fears that she would be embarrassed. But just as Clijsters seemed ready to put the match out of reach, she faltered.

What went wrong? It’s tempting to attribute Clijsters’s second-set collapse to unforced errors. The 19 that she made did not help matters, but it’s worth noting that she made 17 in the first set (compared to 13 in the third). A hitch in her first serve perhaps did more damage. Clijsters made half of her attempts in the second set, compared to 66% in sets one and three. Hingis, who had begun to settle down, won 12 of 16 points off second serves as she ticked off six consecutive games.

Hingis’s strategy was a simple one: Pick on Clijsters’s backhand. Normally the more reliable of Clijsters’s strokes, it was unstable on Tuesday. Clijsters made errors in rallies and off weak serves, giving Hingis the time she needed to work her way back into the match. After Hingis took the second set and broke Clijsters to get back on serve in the third, it looked, for a moment, like luck might be on her side.

It turned out that Hingis needed just a few more gifts than Clijsters was willing to give.At 3-3, 30-30 in the third set, the Belgian forced an error with a strong backhand crosscourt, then followed it with a backhand service-return winner. Her backhand had reappeared, and Hingis could not recover.

As Clijsters moves on, much will be made of the fact that she defeated, and at times battered,Hingis on an off night. Yet this should not deter Hingis as she pushes her three-year retirement further into the past. She can do better against Clijsters and the handful of other women who play her caliber of tennis. Hingis will not beat them consistently – in fact, she may hardly ever do it.Yet it is difficult to imagine that she will not improve her fitness and, one hopes, her serve, in coming months.

Hingis looked fatigued last night. This was her first major tournament in more than three years, and after winning a strenuous fourth-round match this week, she played mixed doubles for an hour and 42 minutes the next day. When she lined up against Clijsters, she had lost some of her bounce. She missed a few routine volleys in the first set and could not adjust her strokes to Clijsters’s pace.

Her serve suffered the consequences, too, and not just the soft second one upon which so much criticism has been heaped (deservedly so). On most nights, Hingis can compensate for the bruising her second serve takes by putting a lot of first serves in the box. While her 90-mph first serve is no weapon, it usually is decent enough to keep her from losing a point after her opponent’s first swing. Against Clijsters, however, she missed first serves at an alarming rate.

In her first four matches at this tournament, Hingis made 73% of her first serves, with an average speed of 89.2 mph. Last night she managed 50% in the first set and 61% for the match. She also threw in six double faults, five more than she had hit in the entire tournament. Considering such poor percentages, one would expect to learn that Hingis was going for more, perhaps fearful that Clijsters would trounce her. She wasn’t. Her average speed for the night on first serves was 89.5 mph, almost identical to her average speed for the week.

If Hingis had increased her first-serve percentage to 72%, won the same percentage of those points (61%), and hit her second serve just as poorly, she would have been expected to win at least three more points in the match, with four double faults, rather than six. As it was, she lost four more points than Clijsters for the match.

Speaking afterwards, Clijsters said she believed Hingis could not just compete against the world’s best, but even return to the top.Yes, Clijsters is a generous soul who often speaks well of her rivals. She was not, however, being too kind. Hingis can compete; she proved that, if nothing else, this tournament. And while she will never be a favorite to win a Grand Slam title, she should become more nettlesome for Clijsters and company as the season progresses.

***

The semifinals have arrived at the Open, and Roger Federer still looks approachable, if not beatable. The world no. 1 escaped another close contest last night, defeating Nikolay Davydenko 6-4, 3-6, 7-6 (7), 7-6 (5).

Give the Russian, seeded no. 5, credit: He played an exceptional match, punishing groundstrokes the whole night and pinning the attack-minded Federer behind the baseline. If only he would have moved in more often. Federer, clearly tired by the end of the evening, prevailed because of fabulous defense and several superb shots on important points,including a swinging return of an overhead that caught Davydenko by surprise (the Russian, who was serving for the set at 5-3, guided an awkward half volley wide, giving Federer two break points). Davydenko would push Federer to the brink – six set points in all, including four in the tiebreaker – but in the end Federer would not miss when it mattered most.

tperrotta@nysun.com