Head and Labuschagne offer a measure of cheer in Australia's parched summer

Baby steps, Australia. Baby steps.

When Marcus Harris cracked a short, wide delivery into point's hands in the first over of the day - having just played the perfect cover drive - it did not bode well. For Harris it was another start not converted; for Australia another batsman out to a soft shot.

In the end, though, Australia's batting did enough to keep them in firm control of this Test. Marnus Labuschagne, with his maiden Test fifty, and Travis Head made career-best scores in the 80s - the first time any home batsman had got that far this season - but the hundred remained elusive.

First it appeared that honour would go to Labuschagne, the bolter at No. 3 in Sydney who has now secured his place at least in the short term, but he chipped the part-time spin of Dhananjaya de Silva to short mid-on for 81. Still, that wasn't far off nosebleed territory this season. Harris' 79 at the SCG was as far as anyone had got before today.

Their stand of 166 for the fifth wicket was also Australia's best since the Sydney Test against England last January when Shaun and Mitchell Marsh added 169. The Marsh brothers are now out of the Test team, uncertain if they'll be back. Australia had managed one century stand in four Tests against India, the 112 that Harris and Aaron Finch put on for the first wicket in Perth.

"It was enjoyable batting out there with Marnie, I thought he batted exceptionally well and left the ball beautifully," Head said. "He obviously knows the Gabba really well and I thought the way he played was outstanding."

The partnership broken, Head, one of two new vice-captains (you can't have too many vice-captains), had the chance to register that mythical three-figure mark. He had looked far less assured than Labuschagne during his innings - skittish against pace and spin, given a life on 29 as Niroshan Dickwella spilled a reasonably regulation catch shortly after the first break when the game could have remained in the balance - but he showed the fighting qualities that Justin Langer so admires.

"I'm there to get runs and bat. I try to lead in that way," Head said of his new role. "It's a nice start today to lead from the front and form that partnership. The other stuff off the field Painey (Tim Paine) is pretty sorted with JL. So leading from the front and on the field is the way I would like to go about it."

Alas, early in the evening session, as the lights started to have full effect he was pinned lbw when Suranga Lakmal - at that moment the only Sri Lanka seamer left standing with Lahiru Kumara and Dushmantha Chameera off the field - bent one back into him with the second new ball. Head reviewed, but on ball-tracking the ball was clipping the bails.

"Everyone goes out trying to get a hundred," Head said. "The bowlers have bowled well, we've had guys have opportunities, two of us had opportunities today - or even three or four guys - to get a big a score and it's disappointing that we missed the chance. I don't think we are far away from a batter getting a big score. It just takes one guy and then we can get that roll on."

It meant that by the end of the day, there had been 113 innings between Australian Test centuries since Usman Khawaja's match-saving 141 in Dubai - an innings that was meant to herald his elevation into the senior ranks of a batting line-up missing two key players.

Yet now, six Tests after that century, Khawaja is the batsman in this team under most pressure following his dismissal to Dilruwan Perera late on the first day. He has a top score of 72 this season, which came in the victory in Perth, but has been unable to impose himself on the bowlers. Much of the bowling he has faced has been excellent, but that's the challenge. Australia will be loath to make more changes before the end of the series. If Khawaja makes the cut for Canberra, it will be a crucial match for him.

There are two batsmen who are all but certain to be back for the Ashes. David Warner will be opening - probably at the expense of Joe Burns - and Steven Smith in the middle order barring a dramatic turn of events (which can't completely be ruled out given the dramatic turn of events that has us in this position). With Labuschagne and Head now buying themselves time with these innings and Kurtis Patterson anointed to the middle order, the spotlight is on Khawaja.

After his hasty call-up Patterson ended up coming in at No. 7 because of Nathan Lyon's nightwatchman stint. Labuschagne's dismissal meant he came in an over before the new ball was due, then had to battle through the period where day turns to night. It was hard work and he had 16 off 67 balls when three crisp boundaries off Chameera showcased his timing. He was then lbw to the impressive Lakmal for his fifth wicket.

In the bigger picture, the fact Australia's innings ended with half an hour to go before the close was ideal. A lead of 179 with a nasty six-over period for the Sri Lanka openers to face. Then Mitchell Starc sprayed the new ball down the leg side, so much so that he was removed from the attack after two overs and replaced by Lyon who found the edge of Lahiru Thirimanne's bat, only for Khawaja to miss the chance at slip.

But, at the very end, Pat Cummins removed Dimuth Karunaratne with the final delivery. The last over of the day was far better than the first for Australia who are massive favourites to win this Test, but it is still a case of baby steps.