While David Warner reinforced his status as a modern-day great with a historic century before lunch yesterday, Matthew Renshaw's unbeaten 167 announced him as the vice-captain's likely long-term partner.

The 20-year-old also rammed home his spot in the side ahead of next month's tour of India. Shaun Marsh, a proven performer in the subcontinent, may be waiting in the wings, but Warner's latest offsider will be difficult to shift.

Renshaw has earned a nickname in the team not for his rate of scoring but for coming out of his shell when he first joined the squad last month and then falling back into it when senior figures Warner and Steve Smith were around.

"The Turtle and the Bull, they call me and Davey apparently," he said last night.

Different strokes for different folks. That was the theme for Australia's openers, whose 10-year age gap is far from the only contrast. 

As with Warner and his former partners Chris Rogers and Ed Cowan, these two may too be called an odd couple, but in reality they complement each other perfectly.

Warner's 18th hundred came up in the final over before lunch. It took until after tea for Renshaw to raise his maiden one, but thanks to both their contributions, different in style but similar in weight, the hosts are in a commanding position.

Renshaw, having joined Phillip Hughes as the only Australians under the age of 21 to post centuries in the past 50 years and the seventh youngest of all time, is still going after batting all day. He will resume alongside Peter Handscomb, 40 not out, and as it stands averaging 96, with Australia closing on a series clean-sweep at 3-365.

The strapping Queenslander may have taken his time early on as Warner raced to his century in 78 deliveries – he was on 25 when he sat down to lunch minutes later – but he opened the shoulders after reaching three figures and even pulled out the party tricks with a reverse sweep off Yasir Shah as he demonstrated in pushing to 150 and beyond that he has the tools.

He said he did not even try to keep pace with Warner in a "whirlwind" first session. "Davey was absolutely smoking them and I was sort of just trudging along on not many," Renshaw said. 

"I was trying not to keep up with him like I have done in the past apparently, he keeps telling me. He plays shots that I can't. I generally don't try too much of copying because that's not my game."

His ton, in his fourth Test, arrived from 201 balls when he turned Yasir to square leg for a single, pumping his fist, the joy on his youthful face evident to the 30,305 spectators fortunate enough to bear witness.

Only minutes earlier, though, there had been momentary doubt about whether he might stay on the ground to complete the milestone after he was clattered by a Mohammad Amir bouncer.

On 91, Renshaw turned his head slightly as the ball reared up and as it struck him flush in the grille he lost his footing. There was concern for him from Pakistan's players and Handscomb, and team doctor Peter Brukner and physio David Beakley attended to him. He was asked questions to test his alertness and cleared to continue after their initial assessment determined that he was not concussed.  

The same couldn't be said for his helmet, which was retired with the grille having been shunted to the left of the lid by the force of the blow. "(The doctor) asked me the score and who the last person out was but I got them pretty right," Renshaw said. "I think I was four runs off the score, so not too bad."

Warner said "there was a lot of concern" for Renshaw in the dressing room. "You never ever want to see a player be struck like that on the grille," he said. "That's the area (of the pitch) that both teams have to look out for. To his credit he got back up and played on."

David Warner became the first Australian batsman since Don Bradman to score a Test century before lunch on the first day as Australia continued their domination of Pakistan at the SCG.

The opener joined one of the most exclusive clubs in the game when he became just the fifth batsman to reach triple figures in the first session of a Test and the first to do so on Australian soil.

Warner's whirlwind innings has given Australia an excellent start to the third Test. After winning the toss, Australia finished at 0/126 at lunch with Warner unbeaten on 100 and Matt Renshaw on 25.

Warner was dismissed just after lunch for 113 when he was caught behind off the bowling of Wahab Riaz.

Warner needed only 78 balls to peel off his 18th Test century - the fourth fastest ton by an Australian - reaching the milestone three minutes before the first break on Tuesday.

He received a standing ovation from an appreciative SCG crowd, many of whom were on the edge of their seats as he closed in on history.

Pakistan's Majid Khan was the last player to achieve the feat in 1976 against a New Zealand attack containing the great Richard Hadlee.

It's been more than 86 years since an Australian batsman did so, way back in the 1930 Ashes series when the peerless Bradman made his famous 334 at Leeds. That innings was the highest by an Australian until Matthew Hayden set a new mark with his 380 against Zimbabwe in 2003.

Australian pair Charles Macartney (1926) and Victor Trumper (1902) are the other two batsmen to reach triple figures in the first session.

Warner said he was not aware of the select company he had joined until he was told by team doctor Peter Brukner during the break.

"I only began to think about it when I was on about 80 and there were 25 minutes to go before lunch," Warner said.

"Basically, I thought I'd just keep working hard to get us into a great position. But with the adrenaline pumping you ride the wave and getting to the hundred was the result."

Warner feasted on some terrible bowling from the Pakistan attack, who have been treated with disdain. Misbah-ul-Haq's bowlers had no answer to Warner, who was particularly strong through point.

He did have a slice of luck, surviving a scare on 30 when he nearly chopped on Imran Khan.