West Coast slipped in a far less convincing second half and the Swans stole the lead with just over a minute to go after Jude Bolton converted from a free kick.
Saturday night's final scores were 12.11 (83) to 11.12 (78).
Adam Hunter, in an otherwise solid return from injury, caught Bolton high 35m from goal, giving him the window to put his side in front.
The Swans kicked 10 goals to West Coast's three after the main break, the second-last of those through Nick Malceski who capitalised on some terrific hard work from Adam Goodes to force the ball forward.
It was typical of the two sides; Quinten Lynch and Amon Buchanan had traded earlier blows after Swan Paul Bevan bannered his name with two goals in three minutes.
West Coast started the match emphatically; six unanswered goals produced a 33-point quarter-time lead after the opening stages suggested the match would be a physical affair.
Goodes was the main target and West Coast's first two goals came within a minute, as defender Mark Nicoski snapped after wandering inside 50 and Daniel Kerr broke from the centre to slam through another.
Cox moved to dominate in the middle and soon another clearance spotted Adam Selwood forward, with his head taken by Goodes.
After a week that saw three players suspended for head-high contact, the Swans star found himself in the umpire's book.
But it didn't deter his impact on the match from there as he collected 21 possessions.
When David Wirrpanda added his first and Kerr struck again with a stunning kick from well outside 50, the momentum was all West Coast's. Then Leo Barry infringed Brent Staker to create the Eagles' sixth.
Brett Jones and Beau Wilkes were good in defence for the home side, but the Swans found theirs in Tadhg Kennelly (25 disposals) to stall the Eagles in the second quarter.
The onballers also enjoyed a brief taste of freedom when Kerr left the ground to have his thigh strapped.
At the 11-minute mark of the term, Jude Bolton opened the Swans' account and sparked to lift his team, though Staker soon found big man Mark Seaby all alone in West Coast's forward 50.
And Andrew Embley, who finished the match with 22 disposals, was inflicting plenty of damage in his role off half-back, with Chad Fletcher (22), Kerr (23) and Lynch (19) also busy.
However, the Swans replied almost instantly through Jarrad McVeigh until Hunter, such a beacon in clashes with the Swans, soared and kicked truly to keep the Eagles 36 points clear.
The third quarter saw the tables turn as the Swans jumped, desperate to salvage their game.
One of a number of courageous marks from Kerr stymied their first attempt but soon Malceski, the game leader with 28 touches, backed in his high-profile knee and drilled a goal from just outside 50m.
The Swans were far more resourceful, and even after play went end-to-end for an O'Loughlin behind, he made amends within minutes.
Tireless midfielder Brett Kirk (21 touches) then threaded a goal after being set up by Goodes and, less than six minutes later, added another after Craig Bolton knocked a hard ball loose.
The Swans were back in it.
Wirrpanda drew first blood in the final term as the Swans, led by Goodes, worked to arrest West Coast's midfielders.
McVeigh's contribution in that area grew and, when he goaled from a tight chance eight minutes into the quarter, the Swans seemed buoyed.
Still West Coast sent the ball forward and, when a long kick from Lynch spilled from Wirrpanda's contest, Staker slammed it through.
That was when Bevan weighed in and the Swans entered another episode with West Coast that they are so familiar with.
Sydney Swans 0.4 2.7 6.9 12.11 (83)
West Coast Eagles 6.1 8.7 8.11 11.12 (78)
GOALS
Sydney Swans: J. Bolton 2, Malceski 2, Bevan 2, McVeigh 2, Kirk 2, Buchanan, O'Loughlin
West Coast Eagles: Staker 2, Wirrpanda 2, Kerr 2, Lynch, Hunter, Seaby, Selwood, Nicoski
BEST
Sydney Swans: Goodes, Kirk, Malceski, Kennelly, J. Bolton
West Coast Eagles: Kerr, Embley, Lynch, Staker, Wirrpanda, Cox
INJURIES
Sydney Swans: Nil
West Coast Eagles: Nil
Reports: Adam Goodes (Sydney Swans) reported by umpire Matthew Head for rough conduct on Adam Selwood (West Coast Eagles) in the first quarter
Umpires: Donlon, Kennedy, Head
Official crowd: 38,802 at Subiaco Oval
The views in this article are those of the author and not necessarily of the clubs or the AFL.
