After the 2-1 win, the Spaniard revealed afterwards how he struggled to contain football's hottest properties.
When asked if he was surprised about how the Dortmund midfield pressed his team, Guardiola told DAZN: "No, not surprised because I faced them when I was at Bayern Munich and they played five at the back.
"The rest of them play that system and the quality of [Mahmoud] Dahoud, [Jude] Bellingham and, of course, the pace of the people up front – the quality is there. We know it was.
"But when you want to press they play long balls. They play long balls to Haaland – Haaland is a b*****d. Link-up [play] is always perfect and they have the pace so we knew it was not easy to control them."