Dortmund lined up with three teenagers in their starting XI at the Allianz Arena and paid the price as Bayern's thirtysomethings Arjen Robben and Franck Ribery dominated, with both men on the scoresheet to add to a brace from Robert Lewandowski.
Former Spain midfielder Alonso felt the experience levels of the respective teams was an irrelevance, however, and paid tribute to the performance levels of his team-mates, who helped restore Bayern's 10-point advantage at the Bundesliga summit.
He said: "I don't think it's about age, it's not about experience, it's about the performance and that's where we were better.
"We tried to contain them as well as possible.
"We have a nice balance and the best is yet to come."
Alonso also denied the league was already sewn up despite their healthy lead over RB Leipzig.
He added: "No, not yet, not until it's mathematically over. We have to keep going, be serious, be professional. That's our job and our duty."
Alonso said of his former team: "We know it's going to be a tough game and we will need to be on top of our game. They are probably the best team in the world and it will be a massive test for us. We are at the Allianz Arena, however, and we want a good result."