The recently dethroned Bundesliga champions picked up three crucial points at Signal Iduna Park and, just as crucially, came through the game without injury worries
The recently dethroned German champions were not at their brilliant best at Signal Iduna Park but an early effort from Marco Reus and a late goal from Robert Lewandowski secured the hosts with the most straightforward of victories.
"We have rarely found the game as easy as we have today," Klopp told the club's official website. "Our first attack brought us the lead and for the next 20 or 25 minutes, we were really great.
"Then we lost our way a bit and Mainz were somewhat stronger. We were lucky that they did not equalise but we have exprienced games like this before so we adjusted a bit during the break and then played an intense second half to win the game.
"Also, nobody got injured, so it's been a perfect day for us."
Defender Marcel Schmelzer was just as enthused by the win, primarily because it ensured that Dortmund will be back in the Champions League next season, irrespective of the outcome of their semi-final showdown with Madrid.
"Yes, that is very important," he told RuhrNachrichten.de. "We have always stressed that this was our primary goal for the season.
"Also, now we don't have to read questions about how we're supposed to beat Madrid when we cannot even focus properly on the league.
"It was always very important to us that we focused fully on the game immediately in front of us, and we managed that today."