Labuschagne and Smith double act has Australia firing, Windies end day 74-0
West Indies trail by 524 runs at stumps after toiling in the field for 152.4 overs in Perth, but their fightback began well, with them ending the day on 74 without loss.
The hosts closed their first innings when Travis Head was bowled for 99 by part-time spinner Kraigg Brathwaite.
"I have felt really good for the last couple of weeks batting and fortunately was able to spend a good time out there yesterday and today," Smith told reporters.
"I was playing each ball on its merits and I felt in good sync from the get-go."
Australia dominated from the outset, with overnight batsmen Smith (200 not out) and Labuschagne (204) peeling off nearly four runs an over in the opening session.
Smith was first to reach a milestone, working spinner Roston Chase (0-140) down the ground for one to equal former great Sir Donald Bradman's tally of 29 test centuries.
Labuschagne continued to ride his luck from the previous day by narrowly evading the slips and gully, with a dropped caught-behind chance giving the 28-year-old another life on 194.
He secured his second test double hundred with a powerful cover drive, but the 350-ball vigil ended two deliveries later when wicketkeeper Joshua Da Silva clasped an outside edge induced by skipper Brathwaite (2-65).
Head took on the role of aggressor after lunch as the top-ranked test side accelerated and the tourists surrendered to the inevitability of a declaration.
Smith tickled Brathwaite away for a quick single after tea to reach 200 and consoled his partner who fell agonisingly close to a ton on the next ball, before Australia ended the innings.
In response, Brathwaite (18 not out) and debutant Tagenarine Chanderpaul (47 not out) successfully negotiated a period of hostile pace bowling to ensure a positive end to the day, albeit with several body blows.
"The job is far from over," Brathwaite said. "It is good to see the fight but we need to continue it tomorrow."
Australia captain Pat Cummins received a polite reception from the crowd when he brought himself on to bowl.
Ex-coach and Perth local Justin Langer denied a rift between the pair last week, after saying unnamed "cowards" in the team had criticised his coaching style via the media.