British light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches didn't complement each other, with frequent clinching disrupting the fight.
The officials scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They win," the victor said in the ringside as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought Parker, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Claims Win in Slow Encounter
His career development has slowed in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors ready to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The spectators' acceptance decreased amid constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester fight to capture the European light-heavyweight title.
The arena fell silent for a extremely emotional memorial before the fight as ten bells sounded in memory of local hero Hatton, who died 46 years old in recently.
It was the first major televised fight night in the location since the passing of Hatton. As the final chime ended, the quiet transitioned to a chant of "there's just one Hatton".
The fighting during the bout reflected the sentiment. Arthur was knocked down by a powerful punch directly to the jaw in the initial stage, rising shakily to his feet on the count of eight.
But the traditional red attire of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was injured quickly, significant bruising appearing under his face as the duo exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the result with official scores of draw, close margin and 115-112, but the two athletes were relentless and courageous, exactly what their idol Hatton represented.
