British light heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a contest where the approaches failed to mesh, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what defines champions? They win," Buatsi commented in the ringside as he was faced disapproval from the spectators.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, merited the decision but the Derbyshire fighter experienced the second setback of his 28-fight career.
The Champion Earns Victory in Slow Match
His career development has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers prepared to take risks in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who operated with a solid defense to narrowly win the better stanzas.
The crowd's patience diminished during regular grabbing, with Parker slipping to the canvas several times during clinches.
The underdog closed well, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent local rivalry contest to win the European light heavyweight championship.
The arena became quiet for a extremely emotional memorial before the fight as ten bells tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in September.
It was the first major televised fight night in the location since Hatton's death. As the last bell disappeared, the silence transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was knocked down by a left hook squarely on the chin in the early round, standing uncertainly to his position on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged soon, heavy swelling forming under his face as the duo exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over 12 rounds.
The victor edged the verdict with official scores of even score, 115-113 and clearer margin, but the two athletes were determined and full of heart, all the qualities their hero Hatton embodied.
