Victory over the bottom-placed side was to be expected from the record German champions, who maintained a nine-point cushion at the top of the table, but Heynckes was not so impressed with the way they went about the job.
"My team know that they didn't play all that well today," said Heynckes, who will leave the club in the summer and be replaced by Pep Guardiola.
"Our play was very slow-moving, not as fluid as we are used to.
"But maybe that's positive. At least we know what we still need to work on.
"The first game (after the break) is always difficult and Furth played very cleverly today, defending very well and making things tight for us, trying to play on the counter-attack.
"Today proved once again that the Bundesliga is not a walk in the park."
Nevertheless, with 16 games of the season remaining, it is looking increasingly unlikely that Bayern will relinquish such an advantage.
"They are a team of perfect individuals," said Furth coach Mike Buskens.
"We had a high hurdle to cross today."
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