UK light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight 10-round fight at the boxing arena.
But Parker had his moments, landing some telling single shots in a fight where the approaches didn't complement each other, with constant grabbing disrupting the fight.
The officials judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They win," Buatsi commented in the ring as he was greeted with disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the victory but the British boxer endured the second setback of his 28-bout professional journey.
Buatsi Earns Win in Uneventful Affair
Buatsi's progress has stalled in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to edge the better rounds.
The audience's tolerance wore thin during frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. However, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to secure the continental championship.
The venue fell silent for a deeply poignant tribute prior to the bout as 10 bells sounded in remembrance of local hero Hatton, who died aged 46 in last month.
It was the first major televised match card in the urban center since the passing of Hatton. As the concluding sound ended, the stillness transitioned to a roar of "there's only one Hatton".
The fighting within the ring equaled the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the initial stage, rising shakily to his footing on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was damaged early, noticeable damage forming under his eye as the duo exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor narrowly won the decision with scoring tallies of draw, 115-113 and clearer margin, but each competitor were determined and full of heart, everything their inspiration the legend represented.
