Port Adelaide has recorded a 13 point win over Port Adelaide is a high scoring match.
With their season on the line Port rallied in the final term to run out victors 20.9 (129) to the Bombers' 17.14 (116).
Ken Hinkley's side is now 7-9, just two wins outside of the top eight, while the Bombers have slumped to their seventh loss in eight games.
Power skipper Travis Boak finished with 28 disposals and three tackles.
Ollie Wines and Robbie Gray had 16 clearances between them thanks to the ruck work from Matthew Lobbe, who had 46 hit-outs.
Brendon Goddard was outstanding for the Bombers with 31 disposals, but it was the game of some of Essendon's more inexperienced players that was most impressive.
In just his 10th game Nick O'Brien had 32 possessions and seven clearances, while draftees Kyle Langford and Jayden Laverde showed plenty of promise, with both kicking a pair of goals.
Drafted at pick No.17 last year, Langford had 14 touches, while Laverde (pick No.20) had five tackles, four marks and 10 disposals.
The Bombers started the game strongly kicking three of the first four goals, their quick ball movement catching the Power unaware.
But as the quarter wore on, Port Adelaide began to gain ascendency at the stoppages, with Lobbe dominating in the ruck early with 13 hit-outs to McKernan's five.
Essendon was quick to add to its 10-point lead at quarter-time, defender Michael Hurley kicking the opening goal of the second term after a poor turnover from Andrew Moore.
But the Power soon got into gear, kicking six of the next seven goals to steal a 14-point advantage late in the second quarter.
Goalsneak Jake Neade had the highlight of the quarter, sidestepping several Bombers to snap a brilliant goal, after crumbing the ball from Chad Wingard's spectacular leap over Michael Hibberd.
The Bombers had the chance to regain the lead at half-time, but were yet again wasteful in front of goal, kicking five behinds in the final six minutes of the quarter to head into the main break eight points down.
In his first game against his former side, Ryder was met with relentless boos from the red and black faithful and it seemed to unnerve him in the first half.
But with the game tied at three-quarter time, Ryder came out firing, kicking the opening two goals of the final term to give Port Adelaide a 13-point lead.
The Dons surged again but a contested mark to Ryder and a truly-struck set shot settled Port's nerves, before Jay Schulz finished the contest with another goal minutes later.
ESSENDON 6.1 8.9 12.12 17.14 (116)
PORT ADELAIDE 4.3 10.5 13.6 20.9 (129)
GOALS
Essendon: Hooker 3, Laverde 2, Langford 2, Daniher 2, Heppell, J Merrett, Goddard, Hurley, Z Merrett, Zaharakis, Browne, Boak, Edwards
Port Adelaide: Ryder 4, Schulz 3, Wingard 3, Neade 2, Boak 2, Ebert, Boak, Westhoff, Lobbe, Gray, Moore, White
BEST
Essendon: O'Brien, Goddard, Stanton, Zaharakis, Heppell, Z Merrett, Browne
Port Adelaide: Boak, Ryder, Wines, Wingard, Gray, Lobbe
INJURIES
Essendon: Howlett (left knee)
Port Adelaide: Nil
SUBSTITUTES
Essendon: Shaun Edwards replaced Ben Howlett in the third quarter
Port Adelaide: Aaron Young replaced Angus Monfries at three-quarter time
Reports: Nil
Umpires: Brown, Nicholls, Ryan
Official crowd: 23,705 at Etihad Stadium
