British light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the techniques didn't complement each other, with constant grabbing spoiling the fight.
The officials judged it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They succeed," the victor commented in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th pro success.
Various analysts felt the challenger, 31, merited the decision but the British boxer suffered the second setback of his 28-fight career.
The Champion Secures Win in Dull Encounter
The fighter's advancement has plateaued in the past few years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to narrowly win the better stanzas.
The crowd's patience decreased during constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but several stanzas were challenging to assess. However, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Tribute Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to secure the continental title.
The arena fell silent for a profoundly moving memorial ahead of the contest as ten bells sounded in honor of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound faded, the silence became a roar of "there's only one Hatton".
The fighting inside the ropes reflected the emotion. Arthur was knocked down by a left hook squarely on the chin in the second round, standing uncertainly to his footing on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured soon, heavy swelling appearing under his orbital area as the fighters exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the verdict with judges scorecards of even score, 115-113 and clearer margin, but each competitor were determined and courageous, all the qualities their hero Hatton stood for.
