Seeking their first pair of successive victories in La Liga since February, Athletic spurned a great chance to open the scoring after only six minutes when Nico Williams fired high into the stands.
The hosts again came close to finding the back of the net soon after as Oihan Sancet hit the post after beating Rui Silva with a deft touch of the ball in the six-yard box, before they then hit the woodwork again in the 17th minute as Iñaki Williams’ audacious curler from the left side of the area flew past Betis’ keeper.
Remarkably, the foot of the post came to Los Verdiblancos’ rescue once again with HT on the horizon, on this occasion preventing Aitor Paredes’ glancing header from breaking the deadlock.
Based on their first-half performance, Betis were not looking likely to improve on their woeful H2H record at the San Mamés after losing on nine of their last 10 visits.
However, against the run of play, the visitors struck first in the 52nd minute when Pablo Fornals’ inconspicuous run into the area allowed him the time and space to fire confidently into the corner of the net beyond Julen Agirrezabala.
It should have been smash-and-grab at its very best shortly after the hour mark but Iker Iosada was expertly denied by Agirrezabala at his near post.
Mercilessly, Athletic made Betis pay for that miss almost immediately with substitute Álex Berenguer needing only five minutes to make an impact, heading home Óscar de Marcos’ cross to set up an intriguing finale.
Berenguer’s equaliser revitalised Ernesto Valverde’s side as another of the Leones manager’s changes, Ander Herrera, saw his initial effort saved by Silva before his rebound was also thwarted.
Despite dominating large spells of the game, and hitting the woodwork on three separate occasions, Athletic were ultimately forced to settle for a draw ahead of their UEFA Europa League clash with PFC Ludogorets.
That point leaves Los Leones sixth in the La Liga table, level on points with seventh-placed Betis, who will also be in European action on the same night, facing NK Celje in the UEFA Conference League.
Flashscore Man of the Match: Iñaki Williams (Athletic Club)