@Duluth first half we had zero line speed, zero energy, even our usually good defenders missed tackles, and then when we did get into a bit more of a pattern, defending our line first at a maul then making tackle after tackle would have sapped them hugely, which we did a few times IIRC.
Mauling and defending for long passages is hugely taxing, more so if you have a few of players with fitness not where it should be.