The home side had come back from 2-0 down to lead 3-2 before the visitors secured a point with 20 minutes left to play.
The away team doubled their advantage at the start of the second half as Dorlan Pabon waltzed into the area to round the goalkeeper and slot home.
Sociedad reduced the deficit moments later thanks to Carlos Vela's powerful finish from inside the area.
The goals continued to flow on 57 minutes as Inigo Martinez was given the space to head in and make the score 2-2.
However, Betis earned a point on 67 minutes as Pabon scored his second goal of the game with a confident finish into the bottom corner.