British light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close ten-round contest at the boxing arena.
But Parker had his moments, delivering effective single shots in a contest where the styles failed to mesh, with excessive holding spoiling the action.
The officials scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi said in the ring as he was faced boos from the crowd.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-fight career.
The Champion Claims Victory in Dull Encounter
His career development has slowed in recent years through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing to take risks in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who utilized a tight guard to narrowly win the cleaner rounds.
The spectators' acceptance diminished during constant clinching, with the challenger going down multiple occasions during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the likes of power puncher David Benavidez, and Russian star Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a terrific all-Manchester contest to secure the European light heavyweight championship.
The stadium grew hushed for a deeply poignant homage ahead of the contest as 10 bells rang in memory of local hero Ricky Hatton, who died 46 years old in recently.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime faded, the stillness gave way to a chant of "there's just one Ricky Hatton".
The fighting within the ring reflected the feeling. Arthur was knocked down by a left hook flush on the jaw in the second round, standing uncertainly to his position on the eight count.
But the traditional red equipment of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage appearing under his eye as the fighters exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
The victor edged the result with scoring tallies of even score, close margin and clearer margin, but both fighters were relentless and brave, exactly what their hero the legend stood for.
