* Midfielder scores dramatic 94th-minute header
* Sevilla through to May 14 final on away goals
* Tie against Valencia ends 3-3 on aggregate (Adds Piatti quotes)
VALENCIA, Spain, May 1 (Reuters) - Sevilla snatched a last-gasp place in the Europa League final when a 94th-minute Stephane Mbia header put them through on away goals after their semi-final against Valencia ended 3-3 on aggregate on Thursday.
Despite going down 3-1 in their second leg at Valencia's Mestalla stadium, Mbia's dramatic late strike set up a final showdown with Benfica on May 14 after the Portuguese club eliminated Italian side Juventus 2-1 on aggregate following a 0-0 draw in Turin.
Sevilla were favourites to advance against their La Liga rivals after winning last week's first leg 2-0 at home but a 14th-minute Sofiane Feghouli effort, an own goal from goalkeeper Beto in the 26th and a Jeremy Mathieu blast 21 minutes from time put Valencia 3-0 ahead on the night and 3-2 ahead overall.
They were just over a minute away from going through to the final when Federico Fazio flicked on a long throw and Cameroon midfielder Mbia rose to crash a header into the net and silence the Valencia fans packed into the Mestalla.
It was a triumph for Sevilla coach Unai Emery, who never completely won over the Valencia fans when he was in charge there from 2008 to 2012, and he celebrated Mbia's goal wildly on the side of the pitch.
"This is a unique experience," Emery said in an interview with Spanish television.
"We don't care who we are playing in the final, we just have to enjoy this," added the 42-year-old former Real Sociedad midfielder.
"Now we have to beat a great team (Benfica) because they have beaten Juve, who are also a great club."
Valencia forward Pablo Piatti struggled for words in a TV interview immediately after the whistle and said he and his team mates were "feeling the pain" and "in a bad way".
"We tried, we gave it everything and they scored against us in the last minute," added the Argentine.
"We are happy with the work we put in but it was pointless in the end."
Valencia made an energetic start in front of their vociferous supporters while Sevilla had clearly opted to play a more patient game and wait for a chance on the break.
The home side forced themselves back into the tie when Feghouli received the ball inside the area and cut inside his marker and his left-foot strike took a slight deflection off a defender on its way into the net.
Valencia were level on aggregate in the 26th minute when Jonas made the most of slack marking to send a powerful header towards goal from a Juan Bernat centre.
Beto could only palm the ball onto the underside of the crossbar and then watch helplessly as it bounced off his back and into the net for what UEFA ruled was an own goal by the Sevilla goalkeeper.
The visitors managed to survive the early onslaught without conceding again and came close to a goal in the 36th when Jose Antonio Reyes met a clever Carlos Bacca backheel at the far post but his close-range effort was blocked superbly by Valencia keeper Diego Alves.
Both sides showed attacking intent in the early stages of the second half before defender Mathieu was quickest to react when the ball ran loose at a corner and the Frenchman left Beto no chance with a powerful shot.
Valencia were moments away from going through when Mbia struck to keep alive Sevilla's chances of repeating their successes in Europe's second-tier club competition from 2006 and 2007, when it was known as the UEFA Cup.
Juve, Inter Milan and Liverpool are the only three sides to have won the UEFA Cup/Europa League three times. (Reporting by Iain Rogers, editing by Pritha Sarkar)