Williams??? opener came after nine minutes of the 2-2 Europa League round-of-32 first-leg draw for the Basque side, who only field players either native to or trained in the region.??
Williams was born in Bilbao to a Ghanaian father and a Liberian mother and joined Athletic???s youth system at 16.
The 20-year-old was handed his debut by Ernesto Valverde in December and has gone on to make three substitute appearances in La Liga.
The ???cantera policy??? has seen the likes of Fernando Llorente, Andoni Zubizarreta and Iker Muniain progress from the youth ranks to the first team.
In 2011 full-back Ramalho became the first black player to feature for Athletic, playing in the 2-1 La Liga win over Sevilla.