British light-heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a tight 10-round contest at the Manchester venue.
But Parker found success, landing some telling single shots in a fight where the styles failed to mesh, with excessive holding disrupting the action.
Two judges scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," the victor said in the arena as he was faced negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers felt Parker, thirty-one, merited the win but the contender experienced the second loss of his 28-match career.
The Champion Earns Win in Dull Affair
His career development has plateaued in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what seems like a last chance - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who worked behind a protective stance to edge the better stanzas.
The crowd's patience diminished amid constant clinching, with Parker going down several times during close exchanges.
The underdog closed well, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the supporting bout, Arthur beat Rea by close verdict in a terrific all-Manchester battle to secure the European light heavyweight title.
The venue fell silent for a profoundly moving tribute ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound ended, the quiet gave way to a shout of "only one Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was knocked down by a left hook directly to the jaw in the second round, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up quickly, heavy swelling forming under his orbital area as the fighters traded powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the decision with judges scorecards of 114-114, 115-113 and clearer margin, but each competitor were determined and courageous, exactly what their inspiration the legend represented.
