While several of Wales’ younger players erupted in celebration after Jarrod Evans’ last-kick penalty sealed a first home victory in more than two years, Tompkins reckons Steve Tandy’s team had escaped with a result they were fortunate to claim.
The Saracens centre - one of the senior figures in the Wales squad - cut a noticeably restrained figure at the final whistle, quietly shaking hands with Japanese players as others leaped around in jubilation.
He says that was a deliberate reflection of his own assessment of the performance — and his empathy for the visitors.
“A little bit,” he said when asked if his behaviour was a sign of experience.
“Also a lot of respect to them. I know how much they were hurting as well and I've been in that situation.
“We got away with one there in how we performed. I was happy but I felt for them. We set high standards and I knew there would be some honest conversations coming back and work to be done.”
Tompkins made clear he had no issue with the wild scenes around him. Many of the squad had never tasted victory for Wales on home soil, and the long drought made the release entirely understandable.
“I don't blame any of them (for celebrating). We hadn't won a home game for two years. You have to enjoy the wins.
“This is fleeting and winning is not easy,” he said.
“I'm so pleased for them and Jarrod as well, to do what he did takes a lot of nerve. So enjoy that moment and remember how hard it is to fight back and learn from it.
“Let the boys enjoy it and then move on. We need to keep that positivity to build something here.”
That blend of realism but also encouragement has become central to Tompkins’ role in a Wales team still finding its identity under Tandy.
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And with world number three New Zealand arriving in Cardiff on Saturday, he believes the Japan match must now serve as a sharp lesson in standards.
Facing the All Blacks - a team Wales have not beaten for 72 years - is an experience he does not take lightly.
“It's intense. You really need to bring your A game,” he said.
“It brings something out in Wales as well in the boys. You don't get to do it much, so it's a real honour.
“We have to up our intensity from last week and hit a level that we've been talking about and training for. We need to put that out on the field and really go at it.”
Tompkins has faced New Zealand only once before - 55-23 defeat in Cardiff, in 2022 - an occasion he remembers vividly.
“I've played them only once before and that was pretty magical, facing the Haka and stuff. It's a privilege to put this jersey on and therefore it comes with responsibility.”
That responsibility, he says, includes striking the right psychological balance: respecting the All Blacks without allowing their reputation to dictate the contest.
“You respect them by giving it everything. You respect the position you've been put in to have the opportunity to go at them. We owe it to ourselves to put everything out there and enjoy the moment.”
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New Zealand arrive in Cardiff after a rare defeat — beaten by England — and Tompkins has no doubt they will respond with ferocity.
“There may be some added spice. They'll be fired right up so you have to match it. It will make it a brilliant game because you know they'll come out strong.”
He has yet to speak to his Saracens teammates who were involved in England’s triumph.
“No, I haven't. Not had the chance to message them yet. I'll be seeing them soon. I don't want to give them too much — Ben Earl's already got a big head! But they also played fantastic and it was a hell of a win for them.”
The scale of Wales’ challenge is underlined by a remarkable statistic: New Zealand have won 33 successive games against them.
Tompkins insists he was unaware of the number — and is unconcerned by it.
“I had no clue about that stat. But you can always be the first. What else do you do?
“We're not going to roll over and give up, especially with the way Steve is with this group, how positive he is and what he's brought in,” he said.
“We are close and I think it's coming. These things do take time, I know that from experience.
“We've got to stick to what we know and I think we'll get there. I really do believe that.”
