The Bavarian club have won only once during their first ever season in the top flight of German football, and Saturday's defeat leaves them four points adrift at the bottom of the table with just nine points in 19 games.
The future is looking particularly bleak and Buskens, who won the UEFA Cup as a player for Schalke, admits it is the lowest point of his career.
"Yes, it is," he said. "And the worst thing is, we have put in so much over the past two and a half years to experience the Bundesliga.
"It hurts when, in such an important game like this, you concede three goals in the second half."
There were all smiles in the Mainz camp, on the other hand, with their coach Thomas Tuchel welcoming an unexpectedly big margin of victory.
"We are very happy with this result," he is quoted as saying by Kicker magazine.
"To win 3-0 is something special for us. We were focused on the job and as soon as we got the first goal, things became much easier and we had the courage and conviction."