UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight 10-round contest at the boxing arena.
But Parker found success, landing some telling single shots in a fight where the approaches didn't complement each other, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi said in the ring as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, 31, should have been awarded the decision but the British boxer suffered the second defeat of his 28-match career.
Buatsi Earns Win in Uneventful Affair
Buatsi's progress has slowed in recent years through contract problems and long spells of lack of fights.
Previously predicted as the future of British boxing, he now stands trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who operated with a protective stance to barely take the cleaner stanzas.
The audience's tolerance diminished amid regular grabbing, with Parker falling to the floor various instances during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to capture the continental title.
The arena fell silent for a extremely emotional tribute prior to the bout as a bell ceremony tolled in honor of local hero Hatton, who passed away 46 years old in September.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a roar of "there's only one Ricky Hatton".
The action during the bout reflected the sentiment. Arthur was knocked down by a powerful punch squarely on the face in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was damaged early, noticeable damage appearing under his orbital area as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity seldom decreased over 12 rounds.
Arthur barely secured the verdict with judges scorecards of draw, close margin and 115-112, but both fighters were determined and full of heart, everything their hero the legend embodied.
