British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight 10-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the techniques didn't complement each other, with frequent clinching disrupting the action.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but what defines champions? They win," the victor stated in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts believed the challenger, thirty-one, merited the victory but the Derbyshire fighter endured the second setback of his 28-bout career.
Buatsi Earns Win in Dull Encounter
His career development has slowed in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who worked behind a protective stance to edge the better rounds.
The crowd's patience diminished during regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
Parker closed well, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester fight to capture the European light heavyweight title.
The venue fell silent for a profoundly moving tribute before the fight as 10 bells rang in memory of local hero Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell ended, the silence gave way to a shout of "only one Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was injured quickly, noticeable damage forming under his orbital area as the duo traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
Arthur narrowly won the decision with scoring tallies of draw, close margin and clearer margin, but both fighters were persistent and brave, exactly what their idol Hatton embodied.
