UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, delivering effective individual punches in a match where the approaches didn't complement each other, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi stated in the arena as he was faced boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th pro success.
Several boxing experts felt Parker, thirty-one, merited the win but the Derbyshire fighter suffered the second loss of his 28-bout career.
Buatsi Claims Victory in Dull Affair
His career development has stalled in recent years through management issues and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to achieve expectations - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers ready to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who utilized a solid defense to narrowly win the more effective periods.
The spectators' acceptance decreased because of regular grabbing, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight championship.
The arena grew hushed for a extremely emotional homage before the fight as ten bells rang in remembrance of the city's native Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the last bell disappeared, the quiet became a roar of "only one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was floored by a left hook flush on the jaw in the initial stage, rising shakily to his footing on the count of eight.
But the red-colored shorts of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was injured early, significant bruising developing under his eye as the fighters landed powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over the full distance.
The victor edged the verdict with official scores of even score, close margin and wider gap, but both fighters were persistent and brave, all the qualities their hero Hatton embodied.
