British light-heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive ten-round contest at the boxing arena.
But Parker found success, delivering effective individual punches in a fight where the approaches didn't complement each other, with excessive holding marring the action.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my best performance but what defines champions? They succeed," the victor commented in the ring as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, merited the decision but the British boxer suffered the second loss of his 28-match career.
The Champion Secures Win in Slow Match
His career development has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a final roll of the dice - under recent support.
He started carefully, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the more effective rounds.
The spectators' acceptance wore thin amid regular grabbing, with Parker going down various instances during grappling.
Parker closed well, but multiple periods were challenging to assess. Although, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Tribute Motivates Local Rivalry Battle
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding all-Manchester contest to secure the continental title.
The stadium became quiet for a profoundly moving memorial prior to the bout as 10 bells rang in honor of Manchester's own Hatton, who passed away 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 disappeared, the silence gave way to a shout of "only one Hatton".
The competition inside the ropes reflected the sentiment. Arthur was floored by a powerful punch flush on the jaw in the initial stage, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged quickly, heavy swelling developing under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the decision with official scores of even score, narrow lead and clearer margin, but each competitor were determined and brave, all the qualities their idol the legend stood for.
