SYDNEY Swans coach John Longmire was left to lament a shocking first half which left his side 48 points behind Fremantle at Domain Stadium on Saturday night.

The visitors fought back superbly, booting seven unanswered goals after half-time before the Dockers kicked a late sealer to win by 14 points.
"In our first half we missed too many tackles, our entries going forward weren't great and they made us pay," Longmire said.

"Fortunately we were able to change it, which was a good sign. We were able to change those areas we needed to but 48 points is a lot to make up and we needed everything going our way.

"We were going pretty well there but (there were) just a couple of little errors in that last quarter." 

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Longmire allayed fears of an ankle injury to Isaac Heeney, saying the young gun had been subbed off at half time purely as a precaution.

One of the keys to the Swans revival after half-time was the return to form of Sam Reid, in the unfamiliar role of a midfielder.

Taking more of an Adam Goodes' roaming role, Reid ended with 22 disposals, 11 marks, five inside-50s and three score assists.

It was the best football Reid has played for some time and signaled that Goodes – who is playing reserves - may struggle to return to the senior side.

"He (Reid) certainly had a very good second half, he played a bit on the wing, he played forward and back, he started to take his marks, he was clean," Longmire said.

"We've always had high hopes that Sam can make that next step as a player. He was able to impact the ball in the air significantly and also on the ground he was able to win some important balls. 

"His second half was a really good start to where he needs to go.

"We believe Reidy is able to play a number of different roles for us - today he was able to play in the midfield so with that size, pace and marking ability it adds another dimension to us.

"We've tried it at different times before and it hasn't worked but it worked better tonight, it was good he was able to have an impact."

Longmire said ensuring the Swans stuck their tackles had been the driver for the second-half turnaround as was better delivery to the forward line.

"Effective tackles is a key stat in football," he said.

"Not just tackling but making sure you stick effective ones and (we had to) make sure we used the ball better going forward. 

"Once we were able to do that … we were able to hit the scoreboard a lot more effectively ... we got a lot of things right in the second half."