As the match deteriorated in the second half, Gold Coast actually won the third quarter, before the visitors kicked three goals to one in the final term.
Longmire said a combination of Gold Coast putting Tom Lynch loose in defence, the slippery conditions, their own poor ball use, and a drop-off in intensity all contributed to the fade-out.
"In the end we won by 50 points, but we had a really strong advantage at half-time and it would have been good to make a bigger advantage in the second half," Longmire said.
The Swans' coach was particularly disappointed with his team's ball use.
They dominated disposals (449-304) and inside 50s (58-39) but were unable to make significant inroads after the second quarter.
"We need to get a bit more reward for our effort and a bit of that was we need to use the ball better going forward," he said.
"If we'd have been a bit more efficient that way, it would have made it a bit easier to score."
He said despite having a comfortable lead and playing a team decimated by injuries to its key players, there was no excuse for not finishing more strongly.
"Teams do it and we had an opportunity today to do it and make the most of that advantage at half-time. We need to keep going," Longmire said.
"AFL footy is tough and you need to make sure you keep going for the full four quarters."