Norris and Piastri finished third and fourth behind Ferrari duo Carlos Sainz and Charles Leclerc in Melbourne after McLaren asked Piastri before halfway to swap positions with Norris.
But while the Australian rued missing out on a podium in front of his home crowd, he conceded the swap was fair because had been allowed to undercut his team-mate earlier in the race, and thereafter Norris was faster on fresher tyres.
"For me, it was completely fair," Piastri said. "He qualified in front of me yesterday, went a bit longer on the first stop and he was catching me and was quicker at that point of the race.
"At that point, I was keeping with Leclerc and Lando was catching both of us, so I was honestly kind of hoping he'd be past me and go and get Charles.
"Of course, at home, I would have loved to be able to stay in third. But for me, that was completely fair."
Norris duly distanced Piastri and closed in on Leclerc, but didn't have enough in the bank to challenge the Ferrari, saying getting undercut in the first round of pitstops is where he lost a chance at finishing second.
Piastri said he was encouraged by McLaren's strong weekend but equally frustrated by his own mistakes. He went off in the penultimate corner in the middle stint, labelling it a "slap on the wrist", and didn't get the cleanest qualifying lap in on Saturday.
"I think for me it's been a strong weekend. A couple of mistakes when it mattered which is a bit frustrating but today's been a solid result," he added.
"A little bit of an off in the middle of the end of the second stint, and grained the tyres a little bit there as well, so just struggled a bit in that part of the race.
"I just couldn't really get them back, so some things to learn and go through and see what I could have done a bit better. Apart from that it was a pretty strong day.
"For me, the biggest surprise was honestly Sergio Perez's pace. I was expecting him to come through and he didn't. So, that's probably a bit of optimism for everyone else on the grid."
