I would say that Lin Dan only utilized 55% of his powers for this match, the main purpose is to delay the match for his teammate to recover stamina.
Lin Dan Game set Match. Lin Dan did a Rafael Nadal fist pump to celebrate his win although.. I don't think it's difficult for him at all, he didn't even use his full powers.
When Lin Dan is in this 'casual' mode, you got to push him real hard, make him fed-up, annoy and frustrate him, even threaten him with defeat, then only will he step up his game; otherwise he's content to simply keeps his nose in front all the way to the finishing line. Only he himself can light up the fire in him.
What's the history? The Japanese have some experience at nerve-wracking team events, if I remember correctly.
Whether Lin Dan wins by 2 measly points or 12 convincing points makes little difference to him; he's not one to crush you if he doesn't feel like it, and that's often the case, unless you yourself crumble.
I was afraid that could have been nasty like Li Xuerui. But fortunately for him, luck was on his side.