British light heavyweight Joshua Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a fight where the styles failed to mesh, with excessive holding disrupting the action.
The officials had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi said 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 memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers felt Parker, 31, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Claims Victory in Uneventful Match
His career development has plateaued in the past few years through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to realize his potential - maybe in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The crowd's patience wore thin because of constant clinching, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher David Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Arthur beat Rea by split-decision in a excellent all-Manchester fight to win the European light heavyweight title.
The venue became quiet for a profoundly moving memorial ahead of the contest as 10 bells tolled in honor of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the silence transitioned to a shout of "only one Hatton".
The competition inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the face in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was damaged early, significant bruising developing under his orbital area as the pair exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
The victor narrowly won the verdict with official scores of 114-114, 115-113 and clearer margin, but both fighters were persistent and courageous, everything their inspiration Hatton embodied.
