British light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a match where the styles never quite clicked, with frequent clinching disrupting the fight.
The officials judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest display but what do champions do? They win," the victor said in the arena as he was greeted with disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers felt the challenger, 31, merited the decision but the Derbyshire fighter endured the second setback of his 28-fight career.
The Champion Secures Victory in Dull Match
His career development has slowed in the past few years through management issues and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with neither fighter prepared to overcommit in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the more effective stanzas.
The crowd's patience diminished because of regular grabbing, with Parker falling to the floor multiple occasions during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to secure the continental belt.
The venue grew hushed for a deeply poignant homage prior to the bout as ten bells rang in memory of Manchester's own Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the final chime faded, the quiet became a shout of "only one Hatton".
The competition during the bout matched the sentiment. The eventual winner was floored by a left hook squarely on the face in the early round, rising shakily to his feet on the referee's count.
But the red-colored shorts of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, heavy swelling forming under his face as the fighters traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over the full distance.
The victor barely secured the verdict with judges scorecards of even score, 115-113 and 115-112, but each competitor were relentless and full of heart, everything their inspiration Hatton stood for.
