The 21-year-old from Canvey Island dragged a sub-60 second final lap from his weary limbs to achieve his sixth personal best of the competition and overhaul the American Chris Huffins as runner-up to the world record holder, Tomas Dvorak of the Czech Republic. It was the first major medal for Britain in this event since the retirement of a certain former world and Olympic champion - Daley Thompson.
Macey, whose main target for the season had been a medal at the European under-23 championships, finished with a new personal best total of 8556 points, with Dvorak scoring 8,744.
As he had staggered with exhaustion at the end of the metric mile, Macey recalled how team mates had called out to him that he had moved up from bronze to silver position.
"I didn't know whether to be sick, cry or just pass out," he said, before describing the effect his sudden rise to prominence had had on his rivals.
"I scared them and showed them that there was someone from Great Britain who was going to be the business again."
He added: "This was the World Junior Championships re-lived, but with a bigger score and on a bigger stage and a sweeter personal victory."
In the course of the competition, Macey had overcome - or just plain ignored - injuries to his elbow, hamstring and ankle, as well as recovering his nerve after his pole snapped while he was vaulting at 4.20 metres. He went on to set a new personal mark of 4.60m. Other personal improvements came in the 100m, the 400m, the 110m hurdles, the javelin and the 1500m.
Following Thompson's reluctant retirement in 1992 the event has moved on to the point where two men have beaten the world record of 8,847 points he set in winning at the 1984 Olympics. But - until the ebullient arrival of this 6ft 5in, 151/2 stone, bleach-blond Essex boy - no Briton has looked capable of competing at the highest level.
Having scored 8,347 points in May - putting himself second on the all- time British list - Macey was clear about his ambitions here: "I want to go out there and mix it with the big boys. I want to show a few people there's a new kid on the block."
His attitude, as much as his deeds in the two days of competition which concluded here night have convinced more than a few people that Britain has a new edition of the People's Daley.
When he spoke lightly about how he took pleasure in winding his opponents up whenever he came across them outside the confines of the competition, there was another Thompsonian flashback.
Daley delighted in psyching his opponents out. And then he would beat them.
"My ambition is to break Daley Thompson's British record."
Macey's attitude has already received a seal of approval from Thompson, who has been advising the Estonian decathlete, Erki Nool, here as well as commenting for BBC TV. "Dean is showing he's a great competitor, and it's all about competition," Thompson said.
Back home in Canvey Island, where Macey lives in a three-bedroom semi with his parents, Alan and Patricia, his 20-year-old sister Marie and his 13-year-old brother Adam - with whom he shares a room - there has been sleepless excitement.
His parents could afford either to watch him at last month's European under-23 championships in Gothenburg - where a fall in the hurdles put him out of contention - or here. "We chose the wrong one," his father said.
As a youngster, Macey played in the same youth side as West Ham's Frank Lampard and had trials with Arsenal. But he does not regret the choice he has now made. "I want to be the best decathlete in the world," he says of his decision. "Footballers can't say that. Only decathletes can say that."
On last night's evidence he is well on his way to his ambition.