UK light heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a contest where the styles didn't complement each other, with excessive holding marring the fight.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They succeed," Buatsi stated in the ring as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Various analysts thought the challenger, 31, should have been awarded the win but the British boxer endured the second defeat of his 28-bout career.
The Champion Earns Triumph in Dull Match
His career development has plateaued in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who worked behind a tight guard to edge the better stanzas.
The audience's tolerance diminished amid constant clinching, with the challenger going down multiple occasions during clinches.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a excellent all-Manchester fight to secure the continental title.
The arena fell silent for a extremely emotional memorial before the fight as 10 bells tolled in memory of local hero Ricky Hatton, who died aged 46 in recently.
It was the first major televised fight night in the location since the passing of Hatton. As the final chime ended, the silence became a shout of "only one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a left hook squarely on the face in the early round, rising shakily to his position on the eight count.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up soon, significant bruising appearing under his orbital area as the pair traded hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the pace seldom decreased over twelve rounds.
The victor barely secured the verdict with judges scorecards of 114-114, close margin and clearer margin, but the two athletes were determined and full of heart, all the qualities their inspiration Hatton stood for.
