The Sevilla head coach spent four years at Valencia before he departed in June 2012, but there was little room for sentiment on Thursday as his current side showed no mercy at the Estadio Ramon Sanchez Pizjuan and now stand on the brink of reaching next month's final in Turin.
Stephane M'Bia and Carlos Bacca struck within three first-half minutes to maintain Sevilla's standing as the top scorers in this season's competition.
The victory was Sevilla's first over Valencia this season, but Emery will not be getting too carried away with the result heading into next week's second leg as their opponents came from 3-0 down in their quarter-final tie with Basel to progress.
A lively opening 15 minutes saw both teams enjoy periods of possession, with the hosts showing good pace in attack, but it was Valencia who had the better sight of goal as Paco Alcacer's long-range effort was pushed away by Beto.
It took until the 27th minute before Sevilla threatened the Valencia goal again as Federico Fazio and Bacca both fired just wide of Vicente Guaita's goal.
Sevilla made their pressure pay in the 33rd minute as M'Bia opened the scoring amid controversial scenes.
Ivan Rakitic's free-kick was flicked on by Daniel Carrico to the Cameroon international at the back post, who, despite being in an offside position, initially miscontrolled the ball before back-heeling it into the net.
Juan Antonio Pizzi's men continued to search for an away goal and saw two fantastic chances go begging late on.
