Lyon delivered the wicket of Mohammad Amir that over.
"Maybe it's a confidence thing ... Smith brings him on when the ball is new, as opposed to being a bit of an afterthought," Warne said, praising Lyon's drift and pace on the Nine Network.
Lyon was then given an odd one-over break but returned to bamboozle Wahab Riaz with a well-flighted delivery that spun sharply between bat and pad.
Mitchell Starc conjured the first of six wickets to fall on the rain-shortened day, with his run-out snapping a 146-run partnership between Azhar Ali and Younis.
Smith was forced to reshuffle his plans late in Thursday's final session because of the absence of Matthew Wade and Matt Renshaw.
Wade took the field at 2.35pm when play finally started but left shortly after and spent most of the day at the team hotel, laid low by a stomach bug.
Peter Handscomb, who has served as keeper for Victoria and Big Bash League side Melbourne Stars, took the gloves in the absence of Wade.
It meant Handscomb, who claimed a couple of impressive catches at short leg during the Boxing Day Test, wasn't available to field under the lid.
Renshaw was given that job and delivered a reminder of why it is so unpopular, copping a nasty blow to the top of his helmet during the final session.
The 20-year-old, who was also hit on the grille during his maiden Test ton on day one, initially remained on the field but came off soon after with a headache.
Renshaw was assessed for concussion and never returned to the fray. That setback meant David Warner was shifted to first slip when Australia took the second new ball.
- AAP