Alexis Mac Allister and Cody Gakpo scored either side of half-time before Conor Gallagher pulled one back for Spurs, only for a sensational long-range effort from Dominik Szoboszlai in stoppage time to seal victory for Iraola's side. The Liverpool boss made 10 changes from his previous team selection and was pleased with how his younger, fresher side responded.
"It's true that I made a lot of changes, but I think I needed to do it because we could see the other day we lacked a little bit of energy, we needed fresh legs," Iraola said. "I'm happy because all the players have given us intensity, have given us aggressiveness.
"I think we've been good in a lot of parts of the game, and also happy because we've deserved the reward to win the game and to have earned the right to be in the next round."
Iraola pointed to Gakpo's contribution as a reminder of the Dutchman's value to the squad, while crediting the senior professionals retained in the side for guiding a youthful team through the occasion.
"Cody gives us not just the goals and the assists, he gives us also some physicality, he gives us calmness on the ball," Iraola said. "Players like him, like Ronald Araújo, Alexis, with a team that was quite young, I think his experience has helped us a lot."
The head coach was particularly encouraged by the contribution of Liverpool's younger players, several of whom were withdrawn late on having emptied the tank.
"I was happy for them. In different positions, different demands," Iraola said. "The best thing is probably that they were tired when I subbed them - Trey Nyoni was cramping, Rio Ngumoha couldn't have run a lot more, James McConnell the same. They've been very energetic, with the willingness of winning the duels."
Asked specifically about Lewis Koumas, Iraola said the youngster's application in training had translated onto the pitch.
"I said it during the week and I say it for a reason. He does it in training every day. He is very clear what he needs to do, what the team needs," Iraola said. "The energy he shows is contagious for the rest - when you see the ones up front giving everything, you are kind of forced to go behind and use the same intensity levels."
On the moment Szoboszlai wound up to strike Liverpool's third, Iraola admitted there was little doubt about the outcome.
"The third goal obviously is a worldie, it's outstanding," he said. "The thing with Dom is, before shooting you are trusting he might score. With other players maybe you are thinking, 'It's too far.' With Dom, everyone is thinking he might score."
Iraola also confirmed Joe Gomez's withdrawal at half-time, on his first appearance of the season as captain, had been planned as part of his return from injury.
"Joe has been doing the recovery process very well, and with him it made sense," he said. "It wasn't set, but the plan was not a lot more than 45."