Daniel Ricciardo had a day to forget as Mercedes drivers Valterri Bottas and Lewis Hamilton qualified quickest in practice for the Emilia-Romagna Grand Prix.
It was also a tough day for Max Verstappen and Charles Leclerc as both drivers ran into trouble in the second session.
Ricciardo finished the first practice session in 10th – three spots ahead of teammate Lando Norris. However, his McLaren teammate got the better of the Australian in the second session, as Norris qualified eighth as Ricciardo languished in 18th position.
"It's really cool to be back on this track. It's pretty awesome," he said. "The day itself was a bit difficult. We've definitely got a few things to work on overnight to get some more out of the car.
"It was a challenging day, but we've got a session in the morning tomorrow to figure it out ahead of quali. We'll try to address the issues today and put ourselves in a good place for tomorrow."
Bottas was quickest round the legendary Imola circuit in both sessions but only just, 0.01 seconds faster than his teammate Hamilton.
"We didn't see the best from Red Bull today but we'll see that in Q3 tomorrow. No doubt they are going to be fast," admitted Bottas.
Hamilton said: "The team worked very hard to understand what happened in the last race where we were weak and to see if we can try to tweak the car for a better set-up," he said.
"I also think the track has come a little bit more in our direction."
Leclerc crashed into a wall at the end of the second session, prompting a red flag and the decision not to restart. Red Bull experienced problems as well Verstappen pulled up with a mechanical problem.
"Something snapped on the rear," Verstappen told his team.
There was a collision between Red Bull's Sergio Perez and the Alpine of Esteban Ocon, but it wasn't caught on the coverage. Both cars were taken off the track during the first session.
Perez had a damaged rear-left tyre while Ocon, on a "slow" lap, had a broken front right.
"The two cars reached the apex at the same time, and just barely touched wheels," according to the stewards' report.
"Both drivers agreed in the hearing that it was an unfortunate miscommunication of timing between them, not helped by the fact that both drivers had limited or no communications with their teams at the time.
"Both drivers agreed that neither was at fault."
They were both back in contention for the second session with Perez clocking the sixth fastest time.
Top 10 Practice times after second session:
1. Valtteri Bottas (FIN/Mercedes) 1min 15.551sec,
2. Lewis Hamilton (GBR/Mercedes) at 0.01sec,
3. Pierre Gasly (FRA/AlphaTauri-Honda) 0.078,
4. Carlos Sainz Jr (ESP/Ferrari) 0.283,
5. Charles Leclerc (MON/Ferrari) 0.82,
6. Sergio Perez (MEX/Red Bull-Honda) 0.86,
7. Yuki Tsunoda (JPN/AlphaTauri-Honda) 0.868,
8. Lando Norris (GBR/McLaren-Mercedes) 0.934,
9. Antonio Giovinazzi (ITA/Alfa Romeo-Ferrari) 0.962,
10. Lance Stroll (CAN/Aston Martin-Mercedes) 1.186,