British light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a close ten-round fight at the boxing arena.
But the challenger found success, landing some telling single shots in a fight where the styles didn't complement each other, with frequent clinching marring the action.
Two judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi commented in the ring as he was greeted with disapproval from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts believed Parker, thirty-one, deserved the victory but the contender suffered the second defeat of his 28-bout professional journey.
Buatsi Secures Triumph in Slow Encounter
His career development has stalled in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter ready to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging 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 worked behind a solid defense to edge the cleaner rounds.
The spectators' acceptance decreased amid constant clinching, with Parker falling to the floor several times during grappling.
Parker closed well, but several stanzas were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Arthur defeated Bradley Rea by close verdict in a excellent local rivalry contest to capture the European light heavyweight belt.
The arena fell silent for a profoundly moving tribute ahead of the contest as ten bells rang in remembrance of Manchester's own Hatton, who succumbed 46 years old in September.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime disappeared, the quiet became a chant of "there's only one Ricky Hatton".
The action during the bout matched the emotion. The eventual winner was floored by a significant blow squarely on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured early, noticeable damage appearing under his eye as the pair exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over 12 rounds.
The victor edged the result with official scores of draw, narrow lead and wider gap, but each competitor were persistent and full of heart, everything their idol Hatton represented.
