The 35-year-old produced a deadly display as the Basque side saw off their Belgian counterparts in an eight-goal thriller.
Aduriz got his first goal of the evening with a close range finish before getting his second from the penalty spot to make it 2-0.
Leon Bailey then got one back for Genk just before the half hour mark, but Aduriz had his third before half-time, once again scoring from the penalty spot.
Genk once again reduced the deficit when Onyinye N'Didi scored six minutes into the second half before Aduriz scored his fourth on 74 minutes with a tidy finish.
Tino Susic then made it 4-3 with just over 10 minutes to go, but Aduriz sealed the victory with his third penalty of the evening deep into stoppage time.
Aduriz scored over 30 goals last season and has already scored 10 in 13 games this season to prove that age, really is, just a number.