UK light heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight ten-round contest at the boxing arena.
But Parker found success, landing some telling clean blows in a fight where the approaches didn't complement each other, with frequent clinching disrupting the contest.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They win," the victor stated in the ringside as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the victory but the British boxer endured the second loss of his 28-bout career.
Buatsi Earns Win in Dull Match
His career development has stalled in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - perhaps in what seems like a last chance - under recent support.
He started carefully, with neither fighter prepared to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who operated with a solid defense to barely take the more effective stanzas.
The audience's tolerance diminished because of constant clinching, with the challenger slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Inspires All-Manchester Fight
In the co-main event, Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to win the European light-heavyweight belt.
The venue grew hushed for a profoundly moving tribute prior to the bout as ten bells sounded in remembrance of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound disappeared, the quiet transitioned to a shout of "there's only one Hatton".
The fighting within the ring matched the emotion. Arthur was floored by a significant blow directly to the face in the second round, standing uncertainly to his position on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was damaged soon, noticeable damage developing under his face as the duo landed powerful shots.
Rea, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor barely secured the result with scoring tallies of even score, close margin and wider gap, but both fighters were relentless and courageous, everything their hero the legend embodied.
