Zhou sets the fastest time on Day 2 of pre-season testing after Russell stops on track
Zhou Guanyu shot to the top of the timesheets on Friday evening in Bahrain, where Mercedes brought out a red flag as George Russell's W14 ground to a halt.
Friday morning saw Carlos Sainz set the early benchmark on C3 tyres of 1m 32.486s, a time that stood at the top of the leaderboards until Max Verstappen emerged in the afternoon. The reigning champion shot to second with his first flying effort and 30 minutes into the afternoon he was at the top.
Under the floodlights, Zhou eclipsed the Dutchman's time by 0.040s when he equipped the soft compound and rounded the circuit in 1m 31.610s, although though his session ended slightly prematurely as his car refused to enter first gear at the end of the pit lane with 10 minutes left.
READ MORE: Sainz leads Sargeant and Alonso on second morning of Bahrain pre-season test
Mercedes hit trouble just before the sun set, with George Russell (P13) coming to a stop with a hydraulic issue. The Briton did not return to action and tallied 26 laps in the afternoon, after Lewis Hamilton set 72 laps for P15. The seven-time champion's morning was briefly interrupted by some floor damage and the resulting repairs.
Fernando Alonso managed more than 130 laps and finished third overall for Aston Martin, ahead of AlphaTauri's Nyck de Vries in P4 and Haas's Nico Hulkenberg, fifth.
Sainz's morning stint saw him end up sixth on the board with 70 laps in the Ferrari, with team mate Charles Leclerc taking over to clock more than 60 laps and finish eighth overall.
Between the Ferraris was Williams' Logan Sargeant, who like Alonso and Zhou drove for the whole day. The rookie driver finished seventh and led the mileage stakes – more than 150 laps under his belt. Sargeant rolled into the pits with 15 minutes remaining and extricated the car, with what seemed to be an electrical issue.
It was later revealed that the team were having Sargeant practise exiting the car in the event of a problem, during which a small electrical issue did spring up.
Oscar Piastri finished ninth in the afternoon with his team mate Lando Norris 16th overall after a productive morning.
READ MORE: Piastri says no extra pressure from last year's contract saga as he enjoys 'great' start to life at McLaren
Alpine's Pierre Gasly rounded out the top 10, 1.5s off top spot, with Haas's Kevin Magnussen 11th and Gasly's team mate Esteban Ocon 12th after lapping 49 times in the morning.
Red Bull's Sergio Perez split the Mercedes having set 76 laps in the morning.
Rounding out the standings was AlphaTauri's Yuki Tsunoda, who managed a session-high 85 laps in the morning before handing the car over to Gasly.
The final day of pre-season testing begins at 1000 local time on Saturday, with live coverage on F1.com.