Little more than two months on from his unanimous decision victory over domestic rival Junior Fa in Auckland, Parker defeated Chisora after two judges scored in his favour 115-113 and 116-111 – the second card a bizarrely wide margin given the evenness of the fight.
Parker suffered a flash first-round knockdown and struggled to combat Chisora's stalking pressure through the first six rounds, but came on in the later rounds as his hand speed and combinations came to the fore.
One judge scored 115-113 in Chisora's favour and a rematch will now be expected to take place.
"I'm getting upset now. I bring everything and this is the treatment I get from boxing," Chisora said. "I think they don't like me… But you know what? I won't let them slow me down. No way. I will go again."
Parker needed to win to secure a new Matchroom contract – this was the last fight of his original deal with promoter Eddie Hearn. With victory, he claimed the vacant WBO intercontinental heavyweight title but, more importantly, maintains his WBO #3, IBF #6, WBC #6 rankings.
The victory improves Parker's record in the UK to two wins, two defeats.
"That was a tough fight. I got caught right in the beginning and just had to dig deep and stay focused. Follow the plan that we had in place. Sway it off a bit. But Derek is a very tough opponent. He came forward and put pressure on me from the beginning and threw big bombs and added a lot," Parker said.
The 29-year-old's career was at a crossroads after switching from trainer Kevin Barry to Irish former middleweight champion Andy Lee, who targeted improving Parker's lapses in concentration during rounds.
Chisora, under the guidance of new trainer Buddy McGirt, came on strong to apply relentless pressure in the opening rounds, handing Parker a flash knockdown inside the first 10 seconds after landing an overhand right that caught the Kiwi on the back of the head.
The aggressive Brit stalked Parker through the first six rounds. Parker was regularly backed up against the ropes with Chisora targeting his body to land telling blows.
As Chisora fatigued from round six on, however, Parker was able to use his jab more effectively to control the distance – using his height and reach advantage – and showcase his hand speed and combination work at times.
The tactics from Parker were clear - be patient, wear the 37-year-old Chisora down and wait for an opening that ultimately never came.
Despite Chisora's obvious fatigue and heavy breathing between rounds, Parker was guilty of a lack of activity. Parker looked good through rounds seven, eight and nine but it appeared an even contest heading into the final round.
Paker caught Chisora in the 12th round to back him up against the ropes, but for some reason did not show a killer instinct to let his hands go, instead standing to admire his work.
In many ways it was another frustrating performance from Parker, not the definitive statement many hoped he would deliver.
In the main undercard fight lightweight champion Katie Taylor defended her WBC, WBO, IBF and WBA titles with a tight unanimous decision win over Natasha Jonas. One judge scored the bout 96-94 in Taylor's favour while the other two had it 95-96.
