Sydney have inflicted a costly defeat on Melbourne, with the Swans upsetting the AFL finals aspirants by 21 points in Cairns.

The Demons failed to consolidate their spot in the top-eight as they dropped their seventh game of the season as the Swans cruised to a 10.7 (67) to 6.10 (46) victory at Cazaly Stadium.

After a last-start confidence-boosting three-point victory over finals contenders St Kilda, Melbourne put together a dismal second quarter on Thursday to trail by 28 points at halftime.

The injury-hit Swans did as they pleased through the middle, with co-captains Luke Parker and Josh Kennedy at their dominant best, as the Demons’ pressure was near non-existent.

Swans youngster Justin McInerney broke through for his first career goal, and quickly added a second just before the main break to stun Simon Goodwin’s team.

Melbourne lifted their intensity in the second half.

However, the Swans’ defensive game stood up as the Demons kicked the solitary goal of the third term.

Parker’s second major three minutes into the last quarter lifted the Swans back out to a 28-point lead before Melbourne began to look threatening.

Ed Langdon had a chance to cut the deficit to nine points with six minutes remaining but the Demons midfielder hooked his set-shot from 25 metres out.

Sydney then immediately switched it down the other end of the ground as small forward Lewis Taylor iced the Swans’ fifth win of 2020.

After starting the match in a golden position to move towards securing only their second finals appearance in 14 seasons, the Demons could find themselves outside the top eight by the end of the round.

Swans defender Callum Mills was a late out due to a calf strain and was replaced by key forward Hayden McLean.

That change allowed Sydney coach John Longmire to switch big man Tom McCartin into defence and McLean to play as a deep forward.

Veteran Demons midfielder Nathan Jones ended the match on the bench with a leg injury.