The 25-year-old netted three times in La Roja's 6-1 demolition of Argentina at the Wanda Metropolitano on Tuesday night, while also playing a key part in another goal.
Isco is pleased to have repaid Lopetegui's faith, but has suggested that he is unhappy with club boss Zinedine Zidane for not using him from the off in games more regularly during an inconsistent campaign for Los Blancos.
"It's the first time I scored three goals and, of course, I am very happy," he told reporters post-match. "When you do not have continuity with your team, the matches with the national team give me life.
"Here I have the confidence of the coach, in Madrid maybe I have not won it. I want to show that I am a good player. Julen shows me confidence with minutes. I do not have the confidence that a footballer needs [at Madrid], maybe the problem is me that I did not know how to win Zidane's confidence."