British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a match where the styles never quite clicked, with excessive holding disrupting the action.
Two judges had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best showing but how do champions respond? They win," Buatsi commented in the arena as he was faced disapproval from the spectators.
The British fighter bounced back after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, merited the win but the British boxer experienced the second setback of his 28-bout career.
The Champion Earns Win in Uneventful Encounter
His career development has stalled in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a calculated early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to edge the more effective stanzas.
The audience's tolerance wore thin amid constant clinching, with the challenger going down multiple occasions during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to secure the European light heavyweight belt.
The arena became quiet for a deeply poignant homage ahead of the contest as ten bells sounded in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the last bell ended, the quiet transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. Arthur was floored by a significant blow flush on the face in the initial stage, getting up unsteadily to his position on the referee's count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was injured quickly, heavy swelling forming under his orbital area as the duo traded hard punches.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
The victor edged the result with judges scorecards of draw, narrow lead and 115-112, but both fighters were relentless and full of heart, exactly what their idol Hatton stood for.
