Hearns - coming out of Detroit's Kronk Gym - had regained the public's imagination after returning to devastating form against Roberto Duran in 1984.
His ruthless demolition of the over-the-hill Panamanian was an indication that the "Hit Man" was back, and back to his imperious best. Hagler had also defeated Duran 12 months prior but received boos and jeers rather than accolades for his unanimous decision victory.
Despite 11 successive world title defences at middleweight, Hagler was without the love and admiration for his craft that Sugar Ray Leonard, Duran and Hearns had received in previous bouts against each other.
The Massachusetts man did not have the maverick ability of Duran. Nor was he the posterboy of boxing like Leonard. His fight with Hearns though was a chance for him to shove two fingers up to the critics who had questioned his lack of appeal to fans and broadcasters in the sport.
In front of an alcohol-fuelled 15,000, who had the privilege of witnessing history in the making, Hagler and Hearns delivered one of the greatest spectacles ever seen inside a boxing ring. Even if it did only last eight minutes and one second.
It is a fight which has been compared to Sugar Ray Robinson's hellacious bout with Jake LaMotta in 1951, otherwise referred to as the Valentine's Day Massacre. From the opening bell, it was an awesome affair which saw Hearns weathering an early storm from Hagler.
Despite Emanuel Steward pleading for his fighter to jab and move, Hearns played fire with fire and struck the first significant punch of the first round - a stinging right uppercut which left Hagler hurt and cut.
Fans had just experienced three minutes of boxing brutality at its best. Returning to their stools, both men were bloodied, bruised and battered. Hearns had bust his hand - an occurring theme for his career - while Hagler was being smothered in Vaseline to cover up blood spilling into his right eye.
In the second round, Hagler stalked his opponent across the ring and had huge success in landing left hooks to Hearns' temple. Leonard - commentating for HBO - raised concerns about Hearns' movement, claiming he looked 'a little rubbery-legged'.
At the end of round two, Harry Greb - British middleweight legend - was one of the three judges scoring the contest and had Hagler leading 20-18. Vegas' Herb Santos was also in agreement with Greb while California's Dick Young had the same margin in favour of Hearns.
The scorecards were irrelevant as fans witnessed a dramatic third and final round. Two rounds of non-stop action had left Hagler's hopes of victory hanging by a thread as the referee broke up the two fighters in the third round to allow the doctor to check the former's cut.
Based on his previous two experiences at Caesars Palace - an underwhelming win over Duran and a controversial draw to Vito Antuofermo - Hagler knew he was on borrowed time and would have to end proceedings almost instantly after being cleared to continue. And that is what he did.
Landing a ferocious right to the temple, Hagler hounded his prey and landed a further two right punches and a left hook to flatten Hearns to the canvas. Despite a spectacular effort to make the nine-count, referee Richard Steele correctly halted the contest.
It was the type of fight and result which made Hagler, Hearns, Duran and Leonard the Fabulous Four.
"I want to give Tommy all the credit in the world. He came out the only way he could if he wanted to take something away from a champion," said Hagler, who had finally won over the crowd for his courageous win.
"I have to say that was my favourite fight and not just because of the excitement, but also the fact I overcame a cut, poor refereeing, and I took the best Tommy Hearns could throw at me.
"I was so worked up, I felt like a monster. I wanted him to get up so badly so I could knock him down again. The way I felt I would have beaten an army that night," said Hagler.
"I can still feel those punches he landed on me and I drink a toast to him every time we meet. I am grateful people remember it as one of the all-time great fights. It was definitely the highlight of my career."
Hearns was full of compliments towards his counterpart.
"What can I say? It happens to the best of us. It hurts. But the man showed his greatness tonight. He came in, took my best shot, and fought his a** off."