Real Madrid defeated Dortmund 3-2 on Saturday, with three goals coming in injury-time - including a superb overhead kick from Kylian Mbappe.
Gonzalo was again on the mark for Real, which had Dean Huijsen sent off in added-time.
The youngster admits he's pinching himself over his success in the tournament, saying afterwards: "It was unthinkable for me to have scored four goals at this stage. I'm happy to have scored another goal, but even more so with the victory, with all the team's work and our place in the semi-finals.
"Arda Güler's pass was a treat, just like Trent's the other day. The coach told us to occupy the spaces well and, to be honest, with that ball, all I had to do was tap it in.
"It's the little things that make the difference. Football is won in both boxes and we're lucky to have Courtois, who is the best goalkeeper in the world. Like today, he's saved us many times before."
Asked about similarities with former Real centre-forward Joselu, he added: "I can also play that role as a finisher in the box. It's not that I want to define myself as just that, I can also contribute a lot more to the team in other situations. But now in that position, as long as I keep scoring goals, I'm doing pretty well."