British light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight 10-round contest at the Manchester venue.
But Parker found success, landing some telling single shots in a fight where the techniques didn't complement each other, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best performance but what do champions do? They win," the victor commented in the arena as he was faced negative reactions from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts felt Parker, 31, deserved the decision but the British boxer experienced the second setback of his 28-bout professional journey.
The Champion Earns Win in Dull Affair
Buatsi's progress has stalled in recent times through management issues and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what seems like a final roll of the dice - under recent support.
He began cautiously, with the two boxers ready to be aggressive in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who utilized a tight guard to edge the better rounds.
The spectators' acceptance diminished during constant clinching, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester fight to win the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional memorial prior to the bout as ten bells tolled in memory of the city's native Ricky Hatton, who died 46 years old in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime faded, the stillness became a chant of "there's just one Ricky Hatton".
The competition inside the ropes equaled the emotion. Arthur was sent to the canvas by a significant blow directly to the chin in the initial stage, standing uncertainly to his footing on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured quickly, heavy swelling forming under his orbital area as the fighters landed punishing blows.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the decision with scoring tallies of 114-114, close margin and 115-112, but both fighters were persistent and courageous, exactly what their hero the legend stood for.
