Sydney produced their best form of the year and dented Port Adelaide's top-four hopes with a dominant 55-point thrashing of the Power at the SCG on Sunday.

The so-far inconsistent Swans came into the match in tenth and needing a win against a highly-rated Port side tipped by many as a top four certainty.

But Sydney bolted out of the blocks and led by 43 points at the first break before coasting to an impressive 18.15 (123) to 10.8 (68) triumph that left them comfortably in the top eight with a 5-4 record.

Port coach Mark Williams was left struggling for answers, but Sydney counterpart Paul Roos was a happy man on a day when the Swans demonstrated their true potential.

"Today was one of those days when everything just seemed to come off," Roos said.

"We just executed really, really well throughout the whole day.

"It was clearly the best we've played this year. I think we've played some good footy this year, but it's the best four-quarter performance."

The Swans kicked 7.1 before Port even looked like scoring and were never threatened from that point on.

Seemingly every player in red and white had a day out, with Jarrad McVeigh, Brett Kirk, Ted Richards, Adam Goodes and Darren Jolly prominent in a stellar all-round display.

They also had an even contribution up forward, with six Swans kicking two goals, including Barry Hall, McVeigh and Jolly.

But it was a very different story for the pitiful Power.

On a dark day, Kane Cornes and Dominic Cassisi put in a reasonable effort and Warren Tredrea and 18-year-old Hamish Hartlett kicked two goals apiece.

"That was one of our worst first quarters for a long time," Williams said.

"Our preparation seemed to be pretty good, we got here early enough, had a bit of a kick on the ground, very similar to how we prepare interstate.

"The last three quarters we were pretty competitive but ... it's very difficult to start like that interstate and think you've got any chance.

"Today we were as bad as we have been."

The Swans finished with 405 possessions, which Roos was certain was a club record during his tenure, compared to 278 for the Power.

Heath Grundy capped a day to remember with surely the mark of the year so far, soaring over Jesse White and Troy Chaplin in the second quarter to snare what Roos labelled the best grab he'd seen in 15 years.

Roos also felt the performance would give his side a timely boost ahead of next week's clash with the Bulldogs at Manuka Oval.

"I think they've got a little bit of belief now hopefully," he said.

"They know how to play, it's just a matter of getting up every single week and that's the hardest thing in footy."

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