One slightly pained smile at the coin toss and the customary post-match handshake was about as convivial as it got between Angelique Kerber and German compatriot Carina Witthöft in Melbourne on Wednesday. The world No1 claimed a 6-2, 6-7 (3-7), 6-2 victory and passage to the third round of her Australian Open defence, but not without her second gruelling battle in as many matches.

Right from the off there was an edge to the contest. Witthöft conceded an early break moments after Kerber’s sun visor had flown off her head in the middle of the crucial point, netting the ball and then making a quite stern protest to chair umpire about the injustice of it all. She was waved off, but struck back immediately with a break of her own.

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Kerber was for the second time in three days a most unconvincing-looking defending champion early in this encounter, struggling mightily on serve and offering up three other break points before Witthöft took advantage. Unfortunately the underdog promptly buried herself in an avalanche of unforced errors.

Still, had you covered up the scoreboards, led a bunch of tennis agnostics to the front row of Rod Laver Arena and asked them which of the pair was the world’s best player, the combined effect of Witthöft’s commanding winners and Kerber’s downbeat body language might have netted some interesting responses.

At one stage an unknowing Kerber had a giant, scary-looking wasp resting on her shoulder, but any other weight was lifted when she broke Witthoeft for a third time to make it 5-2 in the first set, which she wrapped up after 35 minutes and a love service game. By then her opponent had twice as many winners on the board but, more crucially, the same multiple of unforced errors.

Things might have fallen away quickly for world No81 Witthöft in the second set, in which Kerber again broke her immediately in a long, attritional service game, but at 2-1, Kerber lost both her serve and the runaway momentum she had established. The inevitability of the second set tiebreak didn’t necessarily prove it would also be a microcosm of everything that had happened prior. But that it was; Witthöft looked a million bucks when she wasn’t making errors that beggared belief, and three of them gave Kerber a 3-1 buffer.

Then it happened. Kerber lost an acrobatic rally and smashed her racket into the court, and that negativity bled into a double fault, so it was back on level terms. Cue Witthöft wearing her opponent down with a series of hammer blows until Kerber effectively conceded by just sort of drifting her way to mid-court and falling short with a tame sliced drop shot; she had botched six consecutive points to lose the second set and open the door for an upset.

Kerber’s downward spiral briefly continued in the third set when she immediately lost her serve, moving between points therein like a pallbearer. Then, right as her malaise appeared terminal, she roared back to life, breaking Witthöft twice and toughing out a precarious service game to lead 4-1 and unclench her fists ever so slightly.

The favourite broke one final time to win in two hours and eight minutes, but did not shake the feeling this women’s draw remains wide open. At her best, Kerber seems to show that it doesn’t actually matter where you hit the ball as long as you do it hard enough, but on days like this such a scattergun method makes her look one of the more beatable No1’s in living memory. Scant consolation for the impressive Witthöft.

Preceding her on Rod Laver Arena was Venus Williams, whose celebratory post-match pirouette had the highest degree of difficulty of any moment in her 6-3, 6-2 romp over Switzerland’s Stefanie Voegele. Afterwards Williams self-deprecatingly marvelled at the way she has now straddled generations of women’s greats, speaking warmly of the likes of former opponents Steffi Graf and Martina Navratilova, and shook her head that she too has now attained their status of veteran sage.

At the other end of the scale, 17-year-old Australian Jaimee Fourlis came back to earth though not with the thud we expected, beaten 6-2, 6-1 by eighth seed Svetlana Kuznetsova but not disgraced. Even with her right elbow thickly bandaged and the odds stacked against her, Fourlis continued rifling highlight reel winners past the veteran until the end, and never looked out of her depth. It had been an afternoon for plucky losers.