British light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a split decision in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a fight where the techniques never quite clicked, with frequent clinching marring the contest.
The scoring judges scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best performance but what do champions do? They succeed," Buatsi said in the ring as he was met by disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Various analysts believed Parker, 31, should have been awarded the win but the Derbyshire fighter suffered the second setback of his 28-match career.
Buatsi Secures Win in Slow Match
Buatsi's progress has slowed in recent times through contract problems and extended periods 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 appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance decreased because of frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker closed well, but multiple periods were difficult to score. However, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of power puncher Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a excellent all-Manchester fight to capture the European light-heavyweight championship.
The arena grew hushed for a extremely emotional tribute prior to the bout as ten bells sounded in memory of the city's native Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the last bell faded, the stillness gave way to a shout of "only one Ricky Hatton".
The action within the ring matched the emotion. The eventual winner was knocked down by a powerful punch flush on the chin in the initial stage, standing uncertainly to his footing on the referee's count.
But the traditional red shorts of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was marked up early, significant bruising forming under his face as the fighters traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
The victor narrowly won the result with official scores of 114-114, 115-113 and wider gap, but both fighters were relentless and full of heart, exactly what their inspiration Hatton represented.
