The Swans have now lost to the Blues twice this year, the first time back in round six at the SCG where they squandered a final-quarter lead to go down by 16 points.
Carlton has had their measure this year, as have two other top four sides in Geelong and Hawthorn, whose wins both came at the SCG.
Heading into round 13, Longmire's men sat in fifth position on the ladder, just half a game outside of the top four behind Hawthorn but after the Hawks' win over Gold Coast on Saturday, the gap is now six points.
"As we sit here right now we're just short of that top four and we need to get better and we haven't got much time to do it," Longmire said.
The Swans now have six days to turn around their form when they host premier Collingwood at ANZ Stadium next Saturday night.
But it seems a huge task as the gap between the Swans at the top four continues to widen.
"We're trying our hardest to bridge the gap and we certainly haven't bridged it this year at this stage," Longmire said.
"The reality is we play Collingwood next week which is a good thing because you've just got to get back on and get going again."
If the Swans are to have any chance against the Pies, they will need to improve on their efficiency and ball use when going forward.
Despite finishing the match against Carlton with four more inside 50s, the Swans registered a scoring efficiency of just 21 per cent, a stat that will need to be addressed before round 14.
"I thought today we were only in the game for 10 minutes in the first quarter and that was it. It was more about our turnovers and ball use going forward versus their ball use going forward," Longmire said.
"When you look at the game they were very efficient with their ball use and we weren't and that was the thing that really stood out to me, along with Carlton's pressure.
"Carlton's pressure was first class, they applied a lot of pressure and we just didn't use the ball well."
Also a concern for the Swans was key defender Ted Richards limping off the ground in the final quarter.
Longmire confirmed that Richards had been hampered by a sore ankle in the past couple of weeks, but until Sunday had managed to run games out.
He will be monitored through the week but remains in doubt for the Magpies clash.
