George Russell set the fastest time in Practice Two at the Emilia Romagna GP as Mercedes showed signs of improvement ahead of Saturday's Sprint.
Russell finished ahead of the Red Bull of Sergio Perez and Ferrari's Charles Leclerc, with the other Mercedes of Lewis Hamilton fourth.
With qualifying having been held on Friday ahead of the first Sprint of the season, teams were expected to focus solely on their race set-ups in the final practice session.
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It remains to be seen whether Mercedes were merely trying out a racier set-up than their rivals in the first dry conditions of the weekend at Imola, or if the Silver Arrows have actually made ground after their disappointing start to the season.
Max Verstappen, who will start the Sprint at the front of the grid after beating Leclerc to pole during Friday's wet qualifying, was seventh.
There was major concern for McLaren, who were unable to get Daniel Ricciardo out on track due to an issue, while Lando Norris, who starts third in the sprint, had his track time limited by a brake issue as he finished slowest among the drivers who posted lap times.
The only other car that failed to make it on track was the Alfa Romeo of Valtteri Bottas, with the technical issue which forced him to stop in qualifying on Friday yet to have been repaired.
Carlos Sainz, who is under pressure after crashing out of qualifying in front of Ferrari's home fans in Italy, was sixth, behind the Alpine of Fernando Alonso.
Di Resta: Mercedes can't be that encouraged
While Russell and Hamilton's positions on the timesheet were encouraging, the unknown nature of car set-ups and fuel loads in practice leaves major doubt as to whether this was a significant step forward.
It must also be considered that the parc-ferme conditions cars have been placed under between qualifying and the Sprint meant only limited adjustments could be made during P2.
The Sky Sports F1 team offered a range of assessments, with Paul Di Resta's cautious view impacted by severe graining on the Mercedes rear tyres pointed out by Ted Kravitz during the session.
"You can't be that encouraged," Di Resta said. "He [Russell] was using DRS.
"Of course Mercedes are going to be stronger, they get the tyres working - I think that's the most important thing, but if you look at the rear graining, that shows a car that's way out the window.
"They've got work to do. Analyse, get that data back to the factory, come up with new solutions. Being stuck under these parc-ferme conditions, you've just got to explore what you can."
Anthony Davidson said: "If the Mercedes does have this speed all day today in the Sprint, then we should expect them making headway and making their way up through the field.
"With the help of the DRS, you can make overtaking possible. Hopefully these new cars will come into their own and deliver that expectation, but I certainly expect the Ferrari and Red Bull to be the ones to beat come the race."
Naomi Schiff added: "Yesterday Mercedes had a very dismal day, they didn't look too bad out there.
"Their fuel loads might have been good, they might have been on the right tyres at the right time, but I think we'll see something from them today."