"That was my biggest mistake as a rookie. I was hitting him all the time and he was having trouble with it. And then he came over and talked to me a bit. He was like, 'Hey bro, how are you?', and I was like, 'Oh, what a nice guy'. Then he just dropped 20 from there on.
"I told [Thunder assistant coach Mark Bryant] and he said, 'That's a vet move - don't do that, you can't be nice'. And I was like, 'But he's a nice guy'."
Pleasantries will surely be eschewed for the next fortnight.
This will be the third time in five seasons the Thunder and Spurs have met in the playoffs, with the score at one triumph apiece.
The winners this season will advance to a likely conference finals date with the defending champions the Golden State Warriors.
But if Duncan again attempts his unusual brand of reverse trash-talking, Adams has a plan.
"I don't talk to him," he said.
"He tries to talk to me, I'm like stone-faced, looking at something else and just trying to ignore him. That's my game plan."
He needs one. The last time these teams met in the playoffs Duncan and the Spurs won in six. After advancing to the conference finals in his rookie campaign, Adams averaged only 5.0 points and 5.2 rebounds while Duncan averaged a double-double of 17.8 and 10.2.
But much has changed since. Duncan is nearing retirement, with the five-time champion playing a reduced role, and Adams has matured into an elite defender integral to the Thunder's success.
The 22-year-old also illustrated his offensive threat in the Thunder's first-round victory over the Dallas Mavericks, posting career playoff highs of 14 and 15 points.
And asked whether they were a sign of him looking to make an increased offensive impact, Adams joked he had been attempting to add a new weapon to his arsenal.
"I've been working on my threes," he said - his career mark of 0-2 from beyond the arc. "You never know, mate, you never know."