Audi's Ekstroem leads the way in Dakar prologue
The prologue influences the starting order for the first stage, with the top 10 finishers choosing their preferred positions on the road.
Ekstroem was one second faster than nine-time world rally champion Sebastien Loeb (48), driving for Bahrain Raid Xtreme (BRX), with Audi teammate and 14-time Dakar winner Stephane Peterhansel (57) third.
Qatar's defending champion Nasser al-Attiyah (52) was fourth in his Toyota.
Audi had three of its revised RS Q e-tron E2 hybrid cars in the top six, with Spaniard and triple winner Carlos Sainz (60) sixth fastest and 14 seconds behind Sweden's Ekstroem.
The 45th edition of the Dakar will be run entirely in Saudi Arabia for the fourth time and goes coast to coast, ending in Dammam on the Gulf on January 15 after a four-day excursion into the sand dunes of the Empty Quarter.
Audi, whose car features an electric drive with a high-voltage battery and energy converter using renewable fuels, won four stages last year and has set a target of finishing on the podium at least.
The German manufacturer could also become the first to win the gruelling event in an electrified car.
In the motorcycle category, Australia's two-time winner Toby Price (35) posted the fastest time on a KTM and a second ahead of compatriot Daniel Sanders (28) for the GasGas factory team.
Britain's defending champion Sam Sunderland (33) was 10th fastest for GasGas.
The Dakar Rally began in 1978 as a race from Paris across the Sahara to the Senegalese capital but switched to South America in 2009 for security reasons. It moved to Saudi Arabia in 2020.