Racegoers might have been disappointed by the absence of Winx in the Chelmsford Stakes, but Hartnell has made up for it with a stunning display in the Group Two feature.
After connections opted not to run the champion mare on Saturday's heavy track, Godolphin's Hartnell assumed favouritism at $2.05 and gave his supporter no cause for concern.
With Storm The Stars and three-year-old Prized Icon heading the six-horse field, James McDonald stalked the pair to the turn.
And as he went past them in the straight, McDonald had plenty of time to look back just to see if any others could muster a challenge.
They could not, and the margin was 7-3/4 lengths to Grand Marshal ($21) with Storm The Stars ($9.50) another short half head third.
As easy as the win was, McDonald wasn't getting too carried away.
"I think Winx would have come out on top, but this horse is going really well," McDonald said.
"I was really rapt with his first hard run and he's built on that.
"I thought I was on Dundeel again in the Derby. He's pretty good."
McDonald won the 2013 Australian Derby on (It's A) Dundeel by a widening six lengths.
The first hard run for Hartnell this campaign was a second to Winx in the Warwick Stakes (1400m) and he appreciated the extra 200m of the Chelmsford.
Although Hartnell was immediately tightened in Cox Plate markets, trainer John O'Shea indicated Sydney would be his spring focus.
"The Metropolitan has always been his aim but there are a few options," he said.
"The plan has always been to run him in Hill Stakes with a view to going to the Metrop.
"The idea is to keep him in Sydney because he likes to get his toe in the ground and he is more likely to get a softer track in Sydney than Melbourne."
The winner of the 2015 BMW (2400m), Hartnell had an indifferent spring and was hurt in the autumn when he banged a hock.
"It was a great team effort to get him back," O'Shea said.
"He had a lot of things go his way today but we'll take it when it comes because there are plenty of days when it doesn't."
There were few hard-luck stories from the beaten brigade although Kathy O'Hara said the second favourite Prized Icon ($3.80) raced keenly early and didn't finish the race off.
Listed - East Cape Guineas
G3 - Kings Cup
G2 - Resource Recycling Superstars Championship
G3 - Lamb & Hayward 4&5yo Trotting Championship
G2 - Storer Motors Nz Trotting Oaks