Pablo Fornals’ late strike secured a 3-1 aggregate victory, as the English side booked their spot in Prague.
The hosts, unbeaten in 23 home European ties since 2017, looked dangerous from the off, with Jesper Karlsson proving a particular threat as they looked to overturn a one-goal deficit from the first leg.
David Moyes’ side soon snuffed out that early stint though, and started to exert some control, leading to Jarrod Bowen dragging a bobbling shot wide.
Shortly afterwards, only the width of the post prevented the Hammers opening the scoring as Lucas Paquetá dipped onto his left-foot with a drop of the shoulder before curling against the woodwork from the edge of the box.
Saïd Benrahma then fired over from distance, while Yukinari Sugawara had a shot deflected narrowly wide at the other end.
The concern for the visitors was that AZ were dominating possession, and they nearly made that count after the break when Sven Mijnans forced Alphonse Areola into a low save.
Evangelos Pavlidis then had a penalty appeal turned down, while Pantelis Chatzidiakos’ thumping low-drive was turned away as the Dutch outfit desperately looked to up the tempo.
The frantic nature of the final few minutes was reflected in hectic end-to-end football which nearly saw Thilo Kehrer stab into his own net as West Ham received a huge let off.
Nayef Aguerd then scrambled wide with a scuffed shot at the other end and then deep into added time, Fornals burst through midfield and slid into the bottom corner from distance to send the travelling fans berserk, as they booked their place in the final.
Flashscore Man of the Match: Tomáš Souček (West Ham)
