Team-mate George Russell hardly fared any better, being the 12th-fastest driver in the opening hit-out and 11th in the latter.
It marked a continuation of the Silver Arrows' frustrating start to the 2022 campaign, notwithstanding that the squad is second in the constructors' championship at the completion of the first two rounds.
That position in the standings is largely a result of Red Bull's double DNF in Round 1 in Bahrain, and Mercedes team principal Toto Wolff admitted on the way to Albert Park that this weekend would be another “learning race”.
It would seem, however, that few questions about the W13 were answered on the opening day of the Australian Grand Prix.
“Nothing you change on the car makes a difference at the moment, so that's the difficult thing,” said Hamilton, who finished 10th from 16th on the grid last time out in Saudi Arabia.
“You know, you get in [the car] very optimistic and then you make changes, and then it doesn't seem to be wanting to improve.
“We made some changes going into P2, but P1 was better and P2 ended up being a bit harder for me.
“So, I don't know, it's just a tricky car.”
Mercedes has won the last eight constructors' championships, but Russell explained ahead of practice at Albert Park that a rapid bounceback is unlikely given the constraints of F1's cost cap.
Hamilton, too, believes that they are largely stuck with what they have got for the time being.
“I don't think it's going to be tricky to find our way back; there's just not a lot we can do,” remarked the seven-time world drivers' champion.
“This is the way it is, and so we just have to drive with it.
“So, that's just the frustrating thing because you're trying to push, you're trying to catch, and even when you do a decent lap, it's 1.2s down.
“You know, it's just difficult.”
Final practice will be held tomorrow at 13:00 local time/AEST.