British light-heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a match where the techniques never quite clicked, with frequent clinching disrupting the action.
The officials scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best showing but how do champions respond? They succeed," the victor stated in the ring as he was met by boos from the crowd.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the contender endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Slow Match
Buatsi's progress has slowed in recent times through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter ready to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who worked behind a solid defense to barely take the better stanzas.
The audience's tolerance wore thin amid constant clinching, with Parker falling to the floor several times during grappling.
Parker closed well, but several stanzas were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the co-main event, Arthur defeated Rea by divided decision in a excellent Manchester vs Manchester contest to secure the European light-heavyweight title.
The venue grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony rang in memory of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the stillness transitioned to a chant of "there's just one Hatton".
The competition inside the ropes reflected the emotion. Arthur was sent to the canvas by a significant blow flush on the face in the early round, rising shakily to his feet on the count of eight.
But the traditional red shorts of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was damaged soon, noticeable damage appearing under his face as the fighters landed punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor barely secured the decision with judges scorecards of even score, close margin and clearer margin, but the two athletes were relentless and courageous, everything their hero Hatton stood for.
