British light-heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a tight ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a contest where the styles didn't complement each other, with frequent clinching marring the contest.
The scoring judges scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi said in the arena as he was met by negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought the challenger, 31, should have been awarded the win but the British boxer endured the second setback of his 28-match career.
The Champion Claims Triumph in Dull Match
The fighter's advancement has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers prepared to be aggressive in a tentative opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to barely take the cleaner stanzas.
The crowd's patience diminished during constant clinching, with the challenger going down several times during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Arthur overcame Rea by close verdict in a terrific all-Manchester contest to win the European light-heavyweight title.
The arena grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the concluding sound faded, the quiet transitioned to a shout of "only one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was sent to the canvas by a left hook directly to the jaw in the second round, standing uncertainly to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured soon, noticeable damage developing under his eye as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action hardly diminished over the full distance.
Arthur barely secured the decision with scoring tallies of even score, close margin and wider gap, but each competitor were relentless and brave, all the qualities their hero Hatton embodied.
