The Dutch winger claimed Bayern's cup win was tougher than the 4-0 margin indicated while Jupp Heynkes agreed that the visitors proved stubborn opponents in the first half
Claudio Pizarro opened the scoring for the Bavarians but die Roten then had to wait until the second half before belatedly doubling their advantage with Robben grabbing the second, Pizarro then added a third before the hour mark while the Dutch maestro had the final say towards the end.
But the 28-year-old conceded it was not as comfortable as the scoreline suggested.
"Four-nil sounds easy but it was tough, so I'm proud of the lads. We worked very hard," the Netherlands international said after registering his first goals of the season.
Coach Jupp Heynckes agreed that Kaiserslautern were difficult to break down and lauded the resourcefulness of his players.
"You could see my players were utterly determined to make the last 16," the coach told reporters.
"Kaiserslautern put up enormous resistance in the first half. I made a lot of changes, but my team still played as a unit, with plenty of ideas and great discipline."
Rafinha injured himself when making an aerial challenge but the full-back took to Twitter to play down the incident.
He said: "I went to win a ball in the air and when I fell down I got hurt, but it is nothing serious."