After five rounds of Mercedes dominance, the return to Europe on the twisty principality street circuit has been flagged as an opportunity for their rivals with Ferrari tipped as favourites for Sunday's race.
They lived up to their billing with local boy Leclerc delighting the home fans by going quickest in the first run ahead of Hamilton before the positions were flipped in the later session on a warm and sunny afternoon in the principality.
Three-times Monaco winner Hamilton, still hunting his first victory since joining Ferrari before the start of last season, clocke
d one minute 13.026 in the second session, 0.111 ahead of 2024 winner Leclerc.
Leclerc had topped the charts with 1:13.978 earlier in the day, with Hamilton 0.226 back.
Red Bull's Max Verstappen was third in both sessions as he also showed he could be in the mix on Sunday, although his team mate Isack Hadjar had a huge scare in the first practice as he slammed into the safety fencing on the exit of the swimming pool chicane, thankfully walking away unhurt.
Monaco's relatively slow corners and lack of long high-speed straights were expected to negate the power advantage enjoyed by Mercedes who have won all five races this season.
It also meant drivers could worry less about rationing the electrical power from their hybrid engines and focus on handling cars with less downforce and grip than in recent races here.
World championship leader Kimi Antonelli and his Mercedes team mate George Russell flipped fourth and fifth places in the two practice sessions.
It was a disappointing day for McLaren's world champion and 2025 Monaco winner Lando Norris.
He was sixth in the opening practice but stopped early in the second with a power unit problem.
Saturday's qualifying promises to be frenetic with 22 cars starting the first of the three rounds.
The session was twice interrupted by red flags, the first after Red Bull's Isack Hadjar slammed into the safety fencing on the exit of the swimming pool chicane, walking away unhurt.
Aston Martin's Fernando Alonso also went off near the end of the session, damaging the front end of his car.