UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a close ten-round fight at the Co-op Live Arena.
But Parker found success, delivering effective single shots in a contest where the techniques never quite clicked, with frequent clinching spoiling the contest.
The officials judged it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi stated in the arena as he was greeted with boos from the crowd.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, should have been awarded the win but the British boxer experienced the second loss of his 28-fight career.
Buatsi Earns Win in Uneventful Affair
His career development has slowed in recent times through management issues and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to realize his potential - maybe in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter ready to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who operated with a tight guard to edge the cleaner stanzas.
The crowd's patience wore thin during constant clinching, with the challenger going down various instances during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to win the European light heavyweight title.
The venue grew hushed for a profoundly moving tribute before the fight as 10 bells rang in memory of Manchester's own Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound faded, the quiet gave way to a chant of "there's just one Hatton".
The competition during the bout reflected the feeling. The eventual winner was floored by a left hook squarely on the face in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was injured soon, heavy swelling forming under his face as the fighters traded punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over twelve rounds.
The victor narrowly won the result with official scores of even score, narrow lead and clearer margin, but the two athletes were determined and courageous, all the qualities their inspiration Hatton represented.
