"Zenit's result turns out to be good for us, so we must take full advantage in the next two games against the Russian team; all in all, the group is wide open," Defour told reporters.
"I think it was a tight game, with Atletico sitting very deep, not allowing us to find space and create opportunities. We were prepared for that kind of strategy," the 25-year-old told reporters after the game.
"Our first half hour was good and we applied lots of pressure. After the equaliser, our level dropped and ended up conceding another goal."
Atleti top Group G with six points, while Zenit and Vienna sit third and fourth respectively with a point each compared to Porto's three.