Antonelli, who was only sixth fastest and Russell eighth in the first session, said: “Was a massive turnaround with the car, because P1 we struggled a lot.
“It was a good change but of course a lot of work to do because Red Bull is quick, McLaren was up there. Long run felt very strong as well.”
Mercedes trackside engineering director Andrew Shovlin added: “It was a messy first session where we didn’t have the car in the right place. We thought there’d be more grip than there was, but the drivers were a lot happier with the car in the afternoon.
“Not a great lap for George but it was only one lap. If that doesn’t go well you look like you’re off the pace.
“He felt he didn’t have the tyres ready for the start of the lap. A few corners were it looks like he might have underestimated the grip level.”
Antonelli was also in impressive form on the few long-run laps completed in the session, emerging 0.3secs quicker than Norris on average and 0.4secs clear of Russell.
Norris said: “P1 not great. P2 a little bit happier, I am still not very happy with the car, it is still very difficult to drive but we seemed a bit closer, but we are always pretty close on Friday in practice, I think we just show more pace than our competitors. We shouldn’t expect anything differently from normal.”
The world champion confirmed he, like all the drivers, was suffering for the energy-hungry nature of the circuit. This is leading the cars to run out of electrical energy on the straights, meaning the engines go into recovery mode and the cars lose speed long before the end of the straights, a phenomenon known in F1 as “clipping”.
“There is just lack of deployment everywhere,” Norris said. “Every single straight. The worst one is through Blanchimont. We go from almost 320km/h to almost 270km/h because we just have no battery left. Every single straight we’re clipping.”
Max Verstappen’s Red Bull, third fastest on the single-lap qualifying simulation runs, was matched with Antonelli on his long run, when equalised for traffic and length.
Verstappen, who topped the opening session, said: “It has been all right for me, didn’t have big problems, the car has been in quite a good window. You see the real gap but it is nothing shocking, it is expected.
“It is just a bit of a tough track with the energy management, seems like we’re a bit slow on the straight compared to some of our competitors, but balance-wise it was OK.”
Norris is one of a number of drivers who face a grid penalty this weekend, after exceeding his permitted number of batteries.
He is joined by Red Bull’s Isack Hadjar, fifth fastest overall behind Lewis Hamilton’s Ferrari, and Aston Martin’s Lance Stroll.
