UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker found success, delivering effective clean blows in a fight where the approaches didn't complement each other, with excessive holding disrupting the action.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but how do champions respond? They succeed," Buatsi said in the ring as he was met by boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Several boxing experts believed Parker, thirty-one, deserved the win but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Claims Victory in Uneventful Affair
Buatsi's progress has plateaued in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to edge the more effective rounds.
The crowd's patience diminished amid constant clinching, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to capture the continental championship.
The arena fell silent for a extremely emotional memorial ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who died at age 46 in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the final chime disappeared, the stillness gave way to a chant of "there's only one Hatton".
The fighting during the bout matched the sentiment. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the early round, rising shakily to his footing on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was injured early, noticeable damage developing under his eye as the fighters landed hard punches.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the result with judges scorecards of even score, close margin and 115-112, but the two athletes were determined and full of heart, everything their hero the legend represented.
