British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the approaches never quite clicked, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They prevail," the victor stated in the arena as he was faced disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought the challenger, thirty-one, merited the win but the Derbyshire fighter endured the second loss of his 28-bout career.
Buatsi Earns Win in Slow Encounter
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to realize his potential - possibly in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter willing to take risks in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who operated with a protective stance to barely take the cleaner periods.
The audience's tolerance decreased because of regular grabbing, with the challenger going down several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Homage Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester contest to capture the continental belt.
The venue became quiet for a deeply poignant homage before the fight as ten bells tolled in memory of the city's native Ricky Hatton, who died 46 years old in recently.
It was the first major televised match card in the urban center since the passing of Hatton. As the final chime ended, the silence transitioned to a shout of "there's just one Hatton".
The action during the bout equaled the emotion. The eventual winner was knocked down by a powerful punch squarely on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the red-colored attire of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was marked up early, significant bruising developing under his eye as the fighters exchanged hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the intensity seldom decreased over 12 rounds.
The victor barely secured the decision with official scores of even score, 115-113 and 115-112, but the two athletes were persistent and full of heart, everything their hero Hatton stood for.
