The 'Ikale Tahi were pipped 23-21 in Kumamoto last night, having trailed 17-0 just before half-time.
Tonga also gave Argentina a 28-point headstart last week and coach Toutai Kefu was at a loss to explain their sluggish beginnings.
"I don't know, it's a good question. The coaches talked about it straight away post-game - maybe we warm up for too long (laughing), I don't know. It's something we need to look at. I think it's probably just the mental thing because, as you can see, we finish a game really well so definitely an issue for us," Toutai Kefu said.