Piastri surprised by Ferrari pace as Leclerc tops Monaco practice
The Australian, who wound up second fastest, said he had experienced a "very messy day" in his McLaren, including sliding into the barriers in FP2, but added that he felt he had the pace to compete "when we get everything together".
"Ferrari are clearly looking a lot stronger than they have done," said Piastri.
"But for myself it has been a very messy day. I will try and reset for tomorrow because I think the pace is there in the car."
Leclerc, who won last year's race to become the first home winner in Monaco in the modern era of the championship, made light of his own downbeat forecasts to deliver a convincing 'double top' in the two sessions
With team-mate seven-time champion Lewis Hamilton third quickest and only one-tenth of a second down, it was an uplifting day for Ferrari following a disappointing start to the season.
Leclerc clocked a best lap in one minute and 11.355 seconds to beat Piastri by 0.038s, a margin that suggests the champion team are likely to shine again on Saturday.
Hamilton's performance, coming on the back of his fourth place at last Sunday's Emilia Romagna Grand Prix, raised the prospect of him bidding to set another record this weekend – by becoming the first driver to win Monaco for three different teams.
He won for McLaren in 2008 and twice more for Mercedes.
But Leclerc warned Ferrari's passionate fans not to get carried away.
"It is too early," he said.
"Friday in Monaco is a special and very specific kind of day with everyone looking for a reference point. Maybe I am less pessimistic, ok, but I am not convinced the other way either."'It's awesome!'
Hamilton said: "It all went pretty smoothly for me.
"I have a little time to find and Charles was very quick. I am sure there is more to find in my driving."
He added that he enjoyed the thrill of driving the Monaco circuit as much as ever.
"It's amazing, it's awesome," he said.
"The coolest track ever to drive. It’s the most fun, every year it is just such a blast."
Lando Norris in the second McLaren was fourth, ahead of RB rookies Liam Lawson and Isack Hadjar, who endured two heavy brushes with the barriers in a final session interrupted by two red flag stoppages.
"It was a tricky day," said Piastri, who damaged his car's front wing after sliding into the barriers at Ste Devote. "The whole day was up and down.
"When we get everything together the pace is quite good. It's just not proving that easy to do at the moment so there’s some things to look at."
Team-mate Norris, who lies 13 points behind Piastri in the title race, said he found it difficult to get some clean laps at times.
"I felt comfortable from the beginning, but I need to progress more in some areas," he said.'Wake up, it's Monaco!'
His struggles for perfection and trouble with 'traffic', a notorious problem on the tight, sinuous streets of the Mediterranean principality, were echoed by most drivers including four-time champion Max Verstappen of Red Bull.
"I'm quite confident that we can be a lot closer. The Ferraris look very fast and I think they took a big step forward," he said.
"Monaco is always tricky with traffic, but two times today I think it was quite dangerous," he said.
At one point during opening practice Alpine's Pierre Gasly complained of drivers who were dawdling as they learned their way and built-up confidence.
"Wake up! it’s Monaco," the Frenchman said.