But the dark clouds above soon produced thunder, lightning and a heavy downpour, with play abandoned about two hours later.
Smith was unbeaten on 100 off 168 balls, with Mitchell Starc unbeaten on seven.
The skipper's hard-fought century proved to be a saving grace for the hosts after struggling middle-order duo Nic Maddinson and Matthew Wade again failed with the bat.
Maddinson, who was clean-bowled by Yasir Shah for 22, now seems all but certain to lose his spot at No.6 after scoring zero, one and four in his previous two Tests.
And wicketkeeper Wade, who was dismissed for nine, will also come under pressure considering he was selected ahead of Peter Nevill for his batting rather than his keeping.
There was further drama in the afternoon session with Pakistan's double-century maker Azhar Ali copping a nasty blow to the helmet while fielding at short leg.
Azhar crumpled after being struck at full force by a Wade pull shot but was eventually able to get to his feet and walk from the ground.
Usman Khawaja earlier fell agonisingly close to his sixth Test century, dismissed on 97 by Wahab Riaz in the fifth over.
Khawaja had looked primed to make his second Boxing Day Test ton in as many years but Wahab's outswinging delivery found his edge and carried through to wicketkeeper Sarfraz Ahmed.
He and David Warner had combined for a 198-run stand on Wednesday before Warner was dismissed by Wahab for 144.
Peter Handscomb continued his promising start to his Test career before being dismissed by Sohail Khan on 54 shortly before lunch.
Left-arm quick Wahab was the most threatening of the Pakistan bowlers, taking 2-135, while Sohail took 2-86.
More showers are forecast for Melbourne on Friday but the conditions are expected to clear up later in the day.
- AAP
