Fresh off signing a one-year contract extension to take him into an 18th season, the magnificent Gunston, 34, headlined a 19.18 (132) to 5.9 (39) smashing that tightened third-placed Hawthorn's grip on a top-four berth.
The three-time premiership forward booted three goals in the second term then four in the third, with the MCG crowd of 42,509 erupting when he nailed his sixth for his 600th league major.
"It's great to see him performing at a high level after his contract announcement this week," Mitchell said.
"I think the great moment was Ollie Greeves kicking it to him (for the 600th) - laced him out, was just a perfect kick, and I think the smile on Ollie's face made up for the lack of smile on Jack's face.
"But they're the moments you build football clubs around and obviously Jack's been a great of this club and he probably joins a new echelon with the way he's playing at the moment."
An All-Australian last year, Gunston (47 goals) sits fourth in the Coleman Medal hunt despite playing just 13 games due to injury.
Mitchell praised both Gunston and Hawthorn's medical team for their "hard work" and "courage" in managing his body to allow a late-career renaissance.
Gunston also became the VFL/AFL's 37th greatest goalkicker and surpassed former teammate Luke Breust as Hawthorn's seventh all-time greatest goalkicker.
"It's sort of crept up on me a bit," Gunston told Fox Sports of the 600th goal.
"It's something pretty special."
Midfielders Will Day (21 disposals, two goals), Jai Newcombe (28 disposals) and Josh Ward (32 disposals) and brilliant half-back Jarman Impey (37 disposals) were influential and Nick Watson jagged three goals.
Mitchell believes both Impey and Blake Hardwick should be All-Australian.
Seventeenth-placed Essendon had few winners, with Nate Caddy fighting his way to three goals.
Zach Merrett, who was desperate to get to Hawthorn last year and is expected to seek a trade, had 22 touches plus nine tackles.
Injury-plagued Jordan Ridley, also expected to seek a trade, came off with a second-quarter foot injury.
Young gun Sullivan Robey was helped off with a right knee injury suffered in a tackle early in the third term.
Interim coach Dean Solomon said Robey had avoided an ACL tear but he and Ridley will have scans.
Hawthorn's day was soured by a first-quarter concussion to Mitch Lewis, who clashed heads with Archer Day-Wicks when attempting to tackle the Bomber.
A dazed Lewis, who had blood streaming from his right eyebrow, at one point dropped to one knee but was able to walk off and Mitchell said the forward was doing OK.
Lewis, fresh off signing a four-year contract extension, will miss next Saturday's clash with North Melbourne in Tasmania.
Essendon were initially buoyed by last week's win over GWS but Hawthorn - who still hope to add Suns spearhead Ben King to their loaded attack - broke away with six unanswered goals in the second quarter.
Hawthorn led by 45 at halftime, then 74 at three-quarter time before kicking away for their third straight win.
"A good learning experience I reckon. Our inability to defend uncontested marks has been and is still an issue for us," Solomon said.
"Six day turn, we were a little bit sore. But that's no excuse to what we dished up today. We've got to get to work."
Essendon host Adelaide at Marvel Stadium next Sunday.
