The Australian, who's seeking an upturn at the Malaysian track which is hosting the race due to the Middle East conflict, finished only 11th in first practice on Friday but improved to sixth-fastest second time around, with teammate Lando Norris the third quickest.
The improvement persuaded Piastri that McLaren will be in the shake-up for what he's convinced will be a closely-fought qualifying on Saturday after Max Verstappen led the way in FP1 with a 1min 37.520sec circuit and Ferarri's Charles Leclerc was quickest in the second on 1:37.528.
Mercedes, with their new upgrade package, didn't have things their own way as championship leader Kimi Antonelli was eighth (1:38.060) in FP2, just behind seventh-placed teammate George Russell (1:38.020).
Piastri (1:37.899) was adamant McLaren, with Norris clocking 1:37.665 in the second session, had made progress over the day.
"We definitely looked better in FP2 than FP1," the Autralian said. "In FP1 we were struggling a lot, to be honest. Things seemed a bit more positive in FP2.
"But I think it looks pretty, pretty close amongst the top-four teams."
Piastri felt Red Bull, for whom Isack Hadjar was second and Verstappen fourth in FP2 after he'd set the day's leading lap earlier, had looked "very strong" all day while Ferrari were "pretty good" too.
"So everyone's kind of had their turn being reasonably competitive," shrugged the Australian.
"I think we're maybe a tiny step behind, but we made a lot of progress from FP1. So hopefully we can keep that trend going and we'll see where we end up."
Verstappen was disappointed with how his pace dropped off in the second session.
"We started off well. It's just very high deg (degradation). A lot of things to look at with the tyres," said the Dutchman, who won the last Malaysian Grand Prix at Sepang in 2017 before it dropped off the F1 calendar because the government felt it couldn't justify the costs.
Lewis Hamilton, fifth fastest in FP2, got a warning for impeding Audi's Gabriel Bortoleto, with his Ferrari team fined 10,000 euros for the offence after stewards took into account the seven-time champ's revelation that his right-hand mirror had been damaged and the team hadn't given him a radio warning.
