Essendon caused the upset of the AFL season with a stunning four-point win over previously-unbeaten competition leaders Geelong on Saturday night.

Geelong went into the round 15 match at Etihad Stadium as short-priced favourites against the Bombers, who were on a five-game losing streak, but it was Essendon who triumphed 18.7 (115) to 16.15 (111) to claim their first win over Geelong since round 18, 2005.

Running halfback Dyson Heppell was a match-winner for the Bombers along with Jake Melksham, while small forward Angus Monfries kicked three goals.

Paul Chapman kicked two majors for the Cats and was inspirational all night while Steve Johnson's three late goals almost snatched the game for Geelong.

Trailing by 17 points at three quarter time, Geelong kicked 7.3 to 5.2 in a late rally but fell just short in front of 43,806 fans.

Champion onballer Joel Corey was a late withdrawal with a sore achilles and he was replaced side by Tom Gillies.

The fired-up Bombers dominated general play and the contested possessions to shock the Cats who found themselves 15 points down at halftime, 8.4 (52) to 5.7 (37).

Andrew Welsh appeared to strain a hamstring just before halftime and was substituted for Travis Colyer, while Geelong's Daniel Menzel also limped off in the second quarter after a heavy clash in a marking contest.

Essendon assistant coach Mark Thompson was pitted on Saturday night against the Cats for the first time since last year's surprise defection.

Thompson, a former Essendon skipper, had claimed he was exhausted after an 11-year reign as Cats coach which included two premierships.

However as Saturday night's fixture was an Essendon home game, Thompson could be assured of a friendly reception.

The Bombers kicked the first three goals of the third term to jump out to a 33-point lead.

Inspired by creative small forward Mathew Stokes, Geelong booted the next four majors to close within six points following a brilliant snap shot from Paul Chapman but the Bombers steadied with two late goals to give them five for the term to Geelong's four as Essendon took a 17-point buffer into the last quarter.

Geelong travel to Perth next Friday to play West Coast while Essendon host Richmond at the MCG next Saturday night.

Bombers coach James Hird said Welsh, who kicked two goals in the first half before breaking down, was likely to be out for about three weeks.

"I'm very happy with our boys' performance," Hird said following Essendon's sixth win from 14 games this season.

"We've been under the pump losing five in a row.

"There's no doubt our performance last week (against Hawthorn) particularly wasn't good enough.

"For the guys to bounce back is a great credit to the character of the players.

"Particularly for our members and supporters, it just gives them something to hold on to for the year.

"They played some really good football. There's a lot of room for improvement still."

Hird said Thompson and Brendan McCartney, a former Cats assistant coach who joined Thompson at Windy Hill this year, had played huge roles in the win over their old side.

Thompson and McCartney deserved great credit for how they had developed Geelong over the past five years and Hird said he could still see their influence in the Cats' efforts in 2011.

"There was a little bit of Geelong in us tonight in the way that they've been coached and you've got to say it's a good thing because they (Geelong) are a great side and we are hoping to be a good side," Hird said.

Cats coach Chris Scott, who has a 13-1 record in his debut season, said second-game forward Mitch Brown had suffered another shoulder injury.

The 196cm Brown also had a shoulder problem last year.

Scott said the Cats couldn't match Essendon's intensity around the ball early in the match.

"After that we struggled to get back into the game," Scott said.

"But I think all Geelong supporters in particular would love the way our players just fight the game out, even when the game is seemingly lost."

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