Valencia lost 2-1 at Monaco but advanced from their Champions League playoff on an aggregate 4-3 score Tuesday, giving Spain a record five teams in the group stage.
Valencia had won the first leg 3-1, and Alvaro Negredo gave the visiting side a great start in the fourth minute at Stade Louis II.
The former Manchester City striker poached Fabinho's misplaced backpass and stroked an exquisite chipped shot that goalkeeper Danijel Subasic could only watch as it floated over his head before landing in the net.
Andrea Raggi made it 1-1 for Monaco in the 18th minute and Elderson netted in the 75th minute to leave the hosts one goal from forcing extra time.
Two-time finalists Valencia met new owner Peter Lim's objective of returning to the Champions League after a two-year absence.
"In life, you have to suffer to reach one's goals," Valencia coach Nuno Espirito Santo said. "This is the first game of our future. Valencia are a Champions League team. We wanted to be here and here we are."
Already the undisputed power in the Champions League, Spain is now the first country to send five sides to Europe's premier tournament.
Valencia will join defending champions Barcelona, 2014 winners Real Madrid, 2014 runners-up Atletico Madrid and Sevilla -- the first team to qualify by winning the Europa League the previous season -- as the five-team contingent from La Liga in Thursday's group phase draw.
Even before Negredo's great goal, Valencia had gone close to scoring when Subasic stretched his leg to deny Shkodran Mustafi from a corner kick.
But he was helpless to stop Negredo's sublime shot.
Negredo wasted no time after picking up Fabinho's pass as he dribbled forward with his head down before surprising Subasic with a gentle strike from the left side of the area.
"Conceding a goal in the first five minutes wasn't the best thing for a team that needed to turn around a result," Monaco coach Leonardo Jardim said.
After Negredo narrowly missed scoring a second when he shot high in the 10th, Monaco responded against the flow of play as Raggi slotted a ball the defense failed to clear inside the upright.
Valencia, however, remained in control and went close to scoring again through headers by Dani Parejo and Rodrigo Moreno before half-time.
Valencia then faded in the last half hour, and Elderson ensured a tense finale after he finished off a rebound off goalkeeper Matthew Ryan's save from a deflected free kick.
Monaco pressed Valencia into their area but couldn't level the tie.