Celtic kept on top after the break and it looked as though their chances would be helped when the Spanish side’s skipper Javier Jimenez was sent off with just under 20 minutes remaining.
Unfortunately, the 10 men levelled through substitute Ismael Martinez to force a penalty-kick shoot-out. Aidan McIlduff and Fiacre Kelleher both passed up opportunities to settle the showdown and Valencia clinched the last-16 spot when Sivera saved from McCart in sudden death.
Boss McIntyre, speaking on the official Celtic website, said: “I’m immensely proud. We are a young side, the youngest side in the tournament, but I see that as a challenge.
“We have eight or nine players out on loan which is great for the club as they are getting that first-team experience and we have the next group coming through.
“They had a big challenge against a strong side, a very good side, and the way the players prepared for the game, addressed the game and the attitude they showed on the pitch was first class.
“Although it may seem disappointing because of the nature of how the game finished, as long as they learn from it, that is the main thing.”
“Off the ball, we closed them down and never allowed them to play the way they like to. We kept the ball for good periods and created two or three really good chances and could have got that second goal.