Trailing CSKA Moscow 2-0 in their best-of-five quarter-final series, Spaniards Caja Laboral produced their best performance of the season to stay in the tie after thumping the six-times winners 93-72 in front of a partisan home crowd in the Basque country.
Efes emulated Caja's achievement by beating holders Olympiakos Piraeus 83-72 at home to reduce their deficit against the Greek side to 2-1. Both ties will be either levelled or decided on Friday when Caja and Efes again host their opponents.
After a tight first quarter in Vitoria, Caja ran riot and led by 31 points at the end of the third period before CSKA added some respectability to the scoreline with a belated rally.
Nine of Caja's 11 players scored with French guard Thomas Heurtel leading the way with 21 points. Montenegrin forward Milko Bjelica added 15 and Serbia's Nemanja Bjelica chipped in with 13 for Caja, who reached the playoffs after a rollercoaster regular season full of ups and downs.
Efes also dominated from start to finish and nailed eight three-pointers from 15 attempts as Olympiakos struggled to contain their long-range artillery, with former Los Angeles Lakers guard Jordan Farmar burying 17 points for the winners.
Serbia forward Dusko Savanovic and Turkey centre Semih Erden scored 15 each, the latter also collecting nine rebounds.
Real Madrid are through to the Final Four after completing a 3-0 sweep of Maccabi Tel Aviv on Tuesday while Panathinaikos Athens are 2-1 up against Barcelona and meet the 2010 champions at home on Thursday.