UK light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight 10-round fight at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a contest where the techniques never quite clicked, with constant grabbing marring the fight.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They prevail," Buatsi said in the ring as he was faced negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, should have been awarded the victory but the contender suffered the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Uneventful Match
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He began cautiously, with both competitors willing to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a tight guard to narrowly win the better stanzas.
The crowd's patience decreased because of regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
Parker closed well, but several stanzas were difficult to score. Although, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Arthur overcame Rea by split-decision in a terrific all-Manchester battle to capture the continental championship.
The venue grew hushed for a profoundly moving memorial ahead of the contest as a bell ceremony rang in memory of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound disappeared, the stillness gave way to a shout of "there's just one Ricky Hatton".
The competition inside the ropes matched the emotion. The eventual winner was knocked down by a significant blow directly to the chin in the early round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage forming under his face as the pair exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the decision with official scores of even score, 115-113 and wider gap, but the two athletes were determined and brave, everything their hero the legend represented.
