UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a contest where the techniques failed to mesh, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my finest performance but how do champions respond? They win," Buatsi stated in the arena as he was met by boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the win but the Derbyshire fighter suffered the second defeat of his 28-bout career.
Buatsi Secures Win in Dull Affair
Buatsi's progress has stalled in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who operated with a solid defense to edge the cleaner periods.
The audience's tolerance decreased because of constant clinching, with the challenger falling to the floor various instances during close exchanges.
Parker ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a outstanding all-Manchester fight to win the European light heavyweight belt.
The arena became quiet for a deeply poignant homage before the fight as ten bells sounded in remembrance of local hero Ricky Hatton, who died aged 46 in recently.
It was the premier televised match card in the city since Hatton's death. As the final chime faded, the quiet gave way to a shout of "only one Ricky Hatton".
The action within the ring reflected the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the face in the early round, rising shakily to his position on the referee's count.
But the Manchester United-red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured quickly, heavy swelling developing under his eye as the pair landed punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor barely secured the decision with official scores of even score, 115-113 and clearer margin, but the two athletes were determined and full of heart, exactly what their idol Hatton represented.
