The Mexican driver managed to find his way into fifth after Saturday's earlier FP3 session, although brusquely noted that his Red Bull was "nowhere" ahead of the run-in to qualifying.
Although Red Bull made changes to the set-up of his RB20, these were not enough to help Perez progress any further into qualifying and he ultimately shook out in a lowly 18th, only outqualifying the Saubers.
Reflecting on his session, Perez felt that the proliferation of traffic was primarily to blame - but also reckoned that the peeling stickers that had been scrubbed off the wall by passing cars also had an effect.
"It was a disaster because firstly on my lap I encountered a lot of traffic into Turn 6, into 7 and there were some stickers laying down on the apex of 8 so I had to avoid all of that," Perez rued.
"I ended up losing a couple of tenths that would have been enough to get through. I was half a second off P1 so it was just a complete disaster, unfortunately."
Perez was almost two tenths short of breaking through into Q2, having failed to improve sufficiently on his final run of Q1 to dislodge Esteban Ocon's lap time in 15th.
He felt that glimmering signs of progress after FP3 had not been delivered upon, and felt that his weekend was now "over" given the notorious difficulty of passing on the Monte Carlo circuit.
"And basically, the weekend is totally over because here there is no chance to overtake, unfortunately.
"This morning we were finding the light. You know, I was P5. We made some more changes, but unfortunately, there were not enough to come through.
"And it hurts a lot, you know, because I think just by putting normal lap in, it would have been enough, but with the traffic that we encountered, it was really difficult."
