The Finn lead the timesheets by 0.0138s from Hamilton, with Max Verstappen the closest challenger to the Silver Arrows in third.
The Racing Point of Lance Stroll finished in fourth, but the Pink Panthers were further off the pace than many had expected after the race in Hungary. Stroll was 0.7s away from the top, just beating the McLaren of Carlos Sainz.
Charles Leclerc was in sixth, splitting the two McLaren's at their home Grand Prix. Lando Norris was nearly a second down on Bottas, with the Brit sporting a one-off helmet designed by a six-year-old.
Hulkenberg is still getting to grips with his Racing Point but is showing strong improvements after every session, so you would expect the German to be right on the pace as we go into qualifying.
Pierre Gasly rounded out the top ten for AlphaTauri, and the Frenchman has been on the pace all weekend. The former Toro Rosso team appear to be contenders for a top ten start, although with how close the midfield is any little mistake could prove costly.
It was a delayed start to the session for Alex Albon in the other Red Bull car, as the team discovered an electrical issue when starting up the car. This comes after his running was cut short in FP2 due to a heavy crash, with spare parts being delivered to the circuit on Saturday morning,
Bahrain International Circuit - Winter testing
Would you like to stay up to date with the latest Lewis Hamilton and Formula 1 news from GPtoday? Activate free push notifications and be the first to know!