Qatar's dream turned into a nightmare as they became the first hosts in the competition's history to lose their opening game.
Qatar's erratic goalkeeper Saad Al Sheeb brought Valencia down in the box and the ex-West Ham forward stepped up to convert the spot-kick.
It got worse for the hosts as Valencia powered in another header before half-time to leave the Al Bayt Stadium silenced at the break.
Many supporters who had left the stadium at the interval did not return, leaving the ground around half-empty for much of the second period.
It contributed to a flat atmosphere both off and on the pitch, with Romario Ibarra's curling shot being pushed out by Al-Sheeb.
Star men Almoez Ali and captain Hassan Al Haydos were both substituted with 20 minutes remaining, and the side could not muster a shot on target.
Qatar could follow as the second with two challenging games left to play after South Africa was the only host not to make it out of the group stage in 2010
Ecuador, meanwhile, has set themselves up in a superb position to progress, extending their excellent recent form to one defeat in 16 games and keeping a clean sheet in their last seven.
They were the better side and had the ball in the back of the net after 160 seconds, but Valencia's close-range header was ruled for offside by VAR.
Quiet a disappointing opening evening for Qatar.