Lewis Hamilton pipped Valtteri Bottas as Mercedes dominated second practice at the Monaco Grand Prix.
The world champion was just 0.081 seconds ahead of the Finn.
Red Bull's Max Verstappen, second behind Hamilton in first practice, missed much of the second as a result of a water leak and ended up sixth.
Ferrari's Sebastian Vettel was third fastest - but a massive 0.763secs off the pace. Team-mate Charles Leclerc was 10th, struggling with car set-up.
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Vettel also had a near-miss at Turn One, when he locked a wheel on entry and just managed to get the car stopped before hitting the barriers.
There was even worse news for Ferrari on the race-simulation runs later in the session, when Vettel was on average more than a second slower than the Mercedes.
Vettel said: "Tried a lot of things. They didn't really work, so not that productive. Struggling a bit. Lacking a bit of pace compared to Mercedes and struggling to get the tyres to really work, so a bit of work to do."
Leclerc said he was struggling to get the tyres into the right operating-temperature, and had not had any clean laps.
Vettel is wearing a helmet paying tribute to the late Niki Lauda, who died on Monday. It is one of a number of tributes being paid by teams and drivers up and down the grid.
Vettel added: "I would have preferred to do something a bit different here but with his passing it was a nice thing to do. I think it looks quite cool. It is based on his last Ferrari design. Maybe it is nice to take him around for some final laps around Monaco."
Hamilton, who was excused from his media duties on Wednesday following the death of Mercedes non-executive chairman Lauda, said: "It's the dream for every driver to come to Monaco and have a car that you can exploit and utilise your abilities with. I'm really proud of the team and naturally our goal is to try to do something really positive this weekend.
"We've made some small tweaks over the two sessions and during the sessions as well, but I've been quite happy with the set-up.
"Every year we come back here, it gets faster and you really notice it when you're going past the barriers. Coming into Turn 12 (Tabac), you carry so much speed into that corner, and then there's just the wall in front of you; going up the hill to Casino it's the same thing. It's incredibly intense out there and you have to be so focused."
Verstappen had been within 0.1secs of the Mercedes in the first session, and split Hamilton and Bottas on the first runs in the afternoon. But after Red Bull discovered the leak he then spent nearly an hour in the garage.
When the Dutchman got back out on track with about 10 minutes to go, he complained of a lack of grip and could not improve.
His team-mate Pierre Gasly was fourth fastest, 0.820secs off the Mercedes, having been a second slower than Verstappen in the morning session.
"In general, we look alright and the pace was pretty good," said Verstappen. "I got enough laps in to feel confident with the car, we tried lots of set-up changes in both sessions and I'm happy with what we have.
"Mercedes is still very strong and I don't think we can fight them for pole, but there is a big gap between second and third which we should be able to fill in qualifying."
Toro Rosso's Alexander Albon, the Anglo-Thai rookie, was an impressive fifth fastest, continuing his strong showing this season.
"It was a good day for us, it's really fun out there and I like the track a lot," said Albon.
"I think we got the car in the right window, now we just need to study what we've learnt from today, so we can fine-tune the car and get ready for Saturday.
"We made a couple of adjustments for the afternoon session and I like how the car feels. We're cautious that other teams will improve for Saturday but finishing in the top five is a nice feeling."
Haas driver Kevin Magnussen was seventh, ahead of the Alfa Romeos of Antonio Giovinazzi and Kimi Raikkonen and Leclerc.
The McLarens of British rookie Lando Norris and Carlos Sainz were 12th and 13th, while the Renaults of Nico Hulkenberg and Daniel Ricciardo were a lowly 16th and 17th
The other British driver, Williams's George Russell, was 19th, just 0.094secs ahead of team-mate Robert Kubica.