British light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight 10-round fight at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a match where the styles never quite clicked, with frequent clinching disrupting the action.
Two judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best showing but what defines champions? They win," Buatsi stated in the ring as he was greeted with boos from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts felt the challenger, 31, deserved the win but the Derbyshire fighter suffered the second loss of his 28-match career.
The Champion Earns Win in Uneventful Match
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the future of British boxing, he now stands trying to fulfil that early promise - possibly in what seems like a last chance - under recent support.
He started carefully, with the two boxers ready to take risks in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who utilized a tight guard to edge the cleaner periods.
The crowd's patience wore thin amid regular grabbing, with Parker falling to the floor multiple occasions during clinches.
The underdog closed well, but many rounds were difficult to score. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor advances, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Motivates All-Manchester Contest
In the co-main event, Arthur overcame Bradley Rea by split-decision in a terrific local rivalry battle to win the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute before the fight as a bell ceremony sounded in remembrance of local hero Hatton, who died aged 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime faded, the silence gave way to a shout of "only one Hatton".
The fighting during the bout equaled the feeling. The eventual winner was knocked down by a significant blow squarely on the chin in the initial stage, rising shakily to his position on the count of eight.
But the red-colored attire of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was injured soon, noticeable damage forming under his orbital area as the fighters exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor barely secured the result with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were persistent and brave, exactly what their idol the legend represented.
