He heads Swede Fredrik Ahlin by 8.9 seconds with Argentine Miguel Baldoni third, 14.9s adrift.
“My strategy has been to drive steadily and carefully, and to just get the car through the stages without damage,” said Riedemann. “It’s not about speed it’s about driving intelligently. I’m not very experienced on gravel so it’s really tough but I’m learning a lot... it’s been a hard lesson for some of the other drivers.”
Riedemann, from Germany, is one of crop of young stars contesting six rounds of the world championship in identical Ford Fiesta R2s prepared by the British M-Sport organisation and using Pirelli control tyres.
With the stages to the west of the island regarded as some of the toughest they will encounter during the season, crews were braced for a testing day on the sun-baked gravel tracks.
Such was the tough nature of the day’s stages that eight drivers were all forced out after damaging their cars beyond immediate repair striking the same rock on stage four.
Among them was Craig Breen, who was leading for the second event in succession only to retire after contact with the rock broke his car’s sump. Victor Henriksson, second on round one in Portugal, and Dutch driver Timo van der Marel also fell foul of the hazard, as did Matteo Brunello, Andrea Crugnola and Yeray Lemes.
In fact, at the remote service in Siamanna, only seven of the original starters were still in contention: Calle Ward and Miko-Ove Niinemae rolled on stages one and two respectively, a loose oil pipe forced Alastair Fisher’s exit on the first test, while Brendan Reeves stopped with an engine glitch.
Jan Cerny, a 20-year-old from Czech Republic, retired on stage five with broken suspension while Australian Molly Taylor, celebrating her 23rd birthday, stopped following the second Monte Grighini Sud stage.
Egon Kaur, who won the inaugural WRC Academy event in Portugal lost four minutes with an off-road excursion on stage two. However, he was able to continue and set the fastest time on stages four-eight, netting a bonus point for each stage victory. He holds fourth overnight, 1m22.6s off the lead with Russian Sergey Karyakin the only other driver to reach the overnight halt in Olbia in fifth overall.
“It was more difficult than I expected, there have been so many retirements,” said Kaur.