Celtic 0-2 Valencia: We made too many mistakes - Brendan Rodgers
Brendan Rodgers said "basic mistakes" cost Celtic dear after a 2-0 home loss to Valencia in the Europa League.
Goals either side of half-time from Denis Cheryshev and Ruben Sobrino left Celtic's hopes of qualifying for the last 16 in tatters.
And the Celtic manager lamented the self-inflicted wounds from the Scottish champions.
"The lessons are you need to really concentrate, there wasn't a lot in the game," said Rodgers.
"If you take away the two mistakes there wasn't a lot of chances for either side.
"We have to learn from it, we have a lot of young players, and next week if we can get the first goal it can bring a different possibility for us."
Callum McGregor lost possession in midfield as Valencia broke the deadlock on 42 minutes, with Emilio Izaguirre playing the galloping Sobrino onside in the build-up.
Sobrino was then left unmarked to finish Cheryshev's cross from close range early in the second half.
Now Celtic must improve on a poor away record in Europe if they are to overturn the two-goal deficit at the Mestalla in next week's second leg.
"I thought we started the game very well, but Valencia are a team that wait on your mistakes," said Rodgers. "Unfortunately for us we made too many mistakes. When you do that against good teams it kills your momentum, puts you on the back foot.
"Concentration is so important, you can get away with it domestically at times, but at this level, against good players, you don't concentrate and you bring pressure onto yourself. It ended up being a disappointing night for us.
"You have to have that belief [for the second leg]. We've got good players, we might have one or two back as well next week. We need to defend and concentrate well, especially in key moments of the game. If we can get the first goal, it could set us up for a really good second leg."