Championship leader Kimi Antonelli snatched pole position from Max Verstappen in an epic qualifying session at the Monaco Grand Prix.
Antonelli's incredible start to the season continued as he pipped Verstappen by 0.043s with his last run in Q3, where the pole-sitter changed three times in the last two minutes.
Ferrari were big favourites but Lewis Hamilton had to settle for third and Charles Leclerc crashed at the end in his attempt to take another pole on home soil, but will start fourth barring any grid penalties for damage.
George Russell only qualified sixth behind Red Bull's Isack Hadjar and could see his 43-point deficit to Antonelli increase in the Drivers' Championship given the difficulty of overtaking in Monaco.
Russell has largely trailed Antonelli this weekend as the Italian teenager keeps delivering under the highest of pressure and is showing no signs of cracking.
Your Site F1's Martin Brundle said: "We wondered how he would he cope with the pressure finally here in qualifying for Monaco and at such a tender age, with so relatively little experience here. We now have the answer."
McLaren had a disappointing qualifying with Oscar Piastri in seventh and Lando Norris in eighth on a track they were expecting to be more competitive at.
Alpine's Pierre Gasly and Racing Bulls' Liam Lawson made Q3 in an exciting session that only saw one red flag when Gabriel Bortoleto crashed in Q1.
Ferrari's one-twos in both of Friday's practice sessions made them favourites going into Saturday but Mercedes and Antonelli found something overnight to top final practice.
Verstappen was not expected to be in contention as he was nearly one second off the pace but he was second in Q1 and topped Q2 to prove he would be a serious pole threat.
Antonelli took provisional pole after the first Q3 run by 0.001s from Verstappen but Leclerc did not have a representative lap time on the board after making a mistake at Turn 4.
To avoid potential yellow or red flags, Ferrari sent Leclerc out early so the Monegasque driver had the whole track to himself and he went fastest to the delight of the crowd.
But there was still time for others to respond and Verstappen was first to go for it, setting the fastest first sector and powering to provisional pole by two tenths with Hamilton joining him on the front row.
Antonelli, though, landed the last punch with a special Monaco lap to deny Verstappen by 0.043s and, perhaps more importantly, inflict another blow on Russell down in sixth.
"It was one of those laps that we call a magic lap. I was able to put it all together," said Antonelli.
"It was such a close qualifying with Max. The first run of Q3 there was just one millisecond between us.
"But I knew the last lap was good and I was just hoping that it would be enough. It was very close, and I'm very happy with that.
"Massive thanks to the team because yesterday we struggled a little bit and today we were able to improve massively."
Sunday June 7
6.50am: F3 Feature Race
8.30am: F2 Feature Race
10.50am: Porsche Supercup
12.30pm: Monaco GP build-up: Grand Prix Sunday*
2pm: THE MONACO GRAND PRIX*
4pm: Monaco GP reaction: Chequered Flag*
*Also on Your Site Main Event
Watch the Monaco Grand Prix, the first of six races in eight weeks, live on Your Site F1 this weekend.
