Betis were down to nine men just before the hour mark when Lolo Reyes was handed his second yellow card for handball.
It got worse for the home side late on when Guillermo headed home from close range to secure all the points for Bilbao.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
BETIS: Adan; Juanfran, Perquis, N'Diaye, Dídac; Reyes, Nono, Sevilla; Baptistao, Castro, Cedrick
BILBAO: Iraizoz; Iraola, San Jose, Gurpegui, Balenziaga; Rico, Iturraspe, Herrera; Susaeta, Sola, Muniain
3 - Athletic have won two and lost just one of their last four trips to Seville to face Real Betis in La Liga (D1). Hunter.— OptaJose (@OptaJose) February 23, 2014
1 - Ernesto Valverde has only won one of his five previous La Liga meetings with Real Betis as Athletic manager (D3 L1). Experience.— OptaJose (@OptaJose) February 23, 2014