British light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round bout at the boxing arena.
But Parker found success, landing some telling clean blows in a match where the styles never quite clicked, with frequent clinching spoiling the fight.
Two judges judged it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," the victor commented in the arena as he was faced boos from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Various analysts thought Parker, thirty-one, deserved the decision but the British boxer endured the second loss of his 28-bout career.
The Champion Earns Win in Uneventful Encounter
Buatsi's progress has plateaued in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under recent support.
He began cautiously, with both competitors prepared to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The crowd's patience wore thin amid regular grabbing, with the challenger going down multiple occasions during clinches.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester battle to secure the continental belt.
The stadium became quiet for a profoundly moving memorial before the fight as a bell ceremony sounded in honor of local hero Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell ended, the stillness became a chant of "only one Hatton".
The action inside the ropes equaled the feeling. The eventual winner was sent to the canvas by a significant blow flush on the face in the second round, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was injured early, heavy swelling appearing under his eye as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor edged the result with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were persistent and courageous, exactly what their hero the legend embodied.
