In 2008–09, a third place in the regular season meant Alcorcón was allowed to appear in the promotion play-offs for the first time in its history: after disposing of UE Sant Andreu and CD Alcoyano, the club was ousted by Real Unión of Irun in the final round with a 3–1 aggregate.
On 2 January 2008 Oier made his debut for the main squad, in the 2–2 home draw against CD Alcoyano for the season's Copa del Rey.