The Johannesburg side arrived in Pretoria after encouraging early-season wins over defending champions Leinster and the Ospreys.
Those results had raised expectations, but what followed at Loftus Versfeld was a painful reality check. The Bulls ran in nine tries, led 31-10 at half-time, and never looked back in a dominant trans-Jukskei derby display.
Van Rooyen made no attempt to sugar-coat the performance. His focus, however, is already on the response.
"I think it's up to us to make a decision. We can really sulk about this, or we can collectively pull in and make a decision," Van Rooyen said.
"But there's no decision to be made. It's just to get collectively back on the horse and jump on the plane and go fight that battle."
Horn was equally forthright about where the game was lost. The Lions' slow starts have been a recurring issue across their first three matches, and the Bulls punished them ruthlessly in the opening 40 minutes.
"If you give the Bulls 31 points in the first half, with three tries that didn't go past two phases, that puts you under pressure," Horn said.
"That forces you to try things, and you try harder, but sometimes the easy solution is in fact to try less and just do your job better."
The captain was adamant that one afternoon of frustration would not be allowed to dictate the next seven months of the season.
"It would be a shame if the one result determines the whole of the next seven months," he said.
"Knowing the team and knowing the guys that we have, it won't happen.
"We just need to be more focused, more clinical. And if things go a bit bad, just calm down and get cool heads and don't try harder, if that makes sense."