UK light heavyweight Joshua Buatsi earned a win yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a match where the techniques failed to mesh, with excessive holding marring the action.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," Buatsi commented in the ring as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts believed the challenger, 31, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match career.
The Champion Secures Victory in Slow Match
Buatsi's progress has plateaued in recent times through management issues and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with both competitors willing to overcommit in a tentative initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to barely take the cleaner rounds.
The crowd's patience diminished amid frequent holding, with Parker going down several times during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Inspires All-Manchester Battle
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to win the continental belt.
The stadium became quiet for a extremely emotional homage prior to the bout as ten bells tolled in remembrance of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound faded, the quiet transitioned to a roar of "only one Ricky Hatton".
The competition inside the ropes matched the emotion. Arthur was sent to the canvas by a left hook flush on the chin in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, heavy swelling developing under his orbital area as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor narrowly won the decision with judges scorecards of even score, close margin and 115-112, but the two athletes were determined and full of heart, exactly what their idol the legend embodied.
