Piastri starts Sunday's race on pole position, with championship-leading teammate Lando Norris having his work cut out in sixth.
"I'm certainly not shying away from the fact we have the best car at the moment. I think to say otherwise is not correct," the Australian said after Saturday's qualifying at Sakhir.
"But it is difficult and the margins are still pretty tight. It doesn't take much of a mistake to lose one or two tenths, and that's been the gap more or less," he added.
"I certainly don't think we're fast enough to do whatever we want, but we do have a nice advantage at the moment that we're trying our best to make sure we continue to use week in, week out."
Norris won the opener in Melbourne, after Piastri skidded off track and finished ninth, but the Australian triumphed from pole in China.
Red Bull's four-time world champion Max Verstappen ended McLaren's winning run with victory in Japan last weekend, but Piastri could be the first repeat winner of the season.
While Norris struggled to get on top of his car, saying he had been "clueless on track", the Australian saw things very differently.
"It's been a car that's been relatively straightforward to put consistent laps on the board and it's been quick as well, which is obviously the most important thing," he said.
"I've just felt very comfortable this weekend. I think I've felt comfortable the whole season so far with the car we've got, but this weekend has been another step forward on top of that."