Although Ostberg had no expectation that his 27-second overnight advantage over Loeb would be sufficient with two days on asphalt ahead, he only lost 2.3s to the nine-time World Rally champion on the opening 20-kilometre La Mussara stage.
But it all went horribly wrong on the 46km of El Priorat, where Ostberg put his hard tyres on only to find the road was much wetter than he had expected.
That led to frustration, a trip off the road, a brush with a barrier, and a time loss of over a minute for the Adapta Ford.
Loeb and Citroen are not quite assured of victory yet, though, with Jari-Matti Latvala driving superbly to bring the works Ford team back into the hunt after a terrible Friday.
Latvala won La Mussara by 7.1s over Loeb, spooking the champion into "pushing on the limit" on the next stage. Loeb was able to pull out a few seconds on both El Priorat and Riba-Roja d'Ebre to secure a lead of 18.9s heading for service.
Ostberg remains third, but is just eight seconds ahead of Mikko Hirvonen, who has pulled clear of fifth-placed Ott Tanak.
- Sports & Recreation