The 19-year-old Oyarzabal, who also scored a winner to beat leader Barcelona last month, capped his debut campaign by scoring a rebound deep in stoppage time at Mestalla Stadium.

Valencia striker Santi Mina hit the post in the 71st.

Sociedad closed out the season with three straight wins and sits in eighth place before the rest of the final round.

Valencia was left 11th after a fourth consecutive loss to end the season.

Barcelona can repeat as league champion with a win at Granada on Saturday.

If Barcelona drops points, Real Madrid can win the title with a victory at Deportivo La Coruna.