British light heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive 10-round bout at the Manchester venue.
But Parker found success, landing some telling single shots in a match where the techniques never quite clicked, with excessive holding disrupting the fight.
Two judges judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my best performance but what do champions do? They succeed," the victor stated in the ring as he was greeted with boos from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers thought the challenger, thirty-one, should have been awarded the victory but the contender experienced the second loss of his 28-match career.
The Champion Secures Win in Dull Affair
The fighter's advancement has plateaued in the past few years through management issues and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective stanzas.
The audience's tolerance decreased during constant clinching, with the challenger going down multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Fuels Local Rivalry Contest
In the secondary fight, Arthur beat Bradley Rea by close verdict in a terrific all-Manchester battle to capture the continental title.
The stadium fell silent for a deeply poignant memorial prior to the bout as 10 bells sounded in honor of the city's native Hatton, who died at age 46 in last month.
It was the first major televised match card in the urban center since the passing of Hatton. As the final chime faded, the silence became a shout of "only one Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a significant blow flush on the face in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was marked up quickly, heavy swelling appearing under his orbital area as the duo exchanged powerful shots.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur barely secured the result with judges scorecards of even score, 115-113 and 115-112, but each competitor were persistent and brave, everything their idol Hatton represented.
