That was the Englishman's coming-of-age-fight, and it happened in front of 90,000 supporters and a worldwide audience of millions. Parker would have been ringside too had Fury not delayed their original April 1 fight date and then fail to turn up at all, but despite his distance to those life-changing events in London, he will get his chance soon.
Asked about his determination to make a statement against Cojanu, Parker said: "It will help big time but I guess it's not about that. For us, we're just focusing on what we want to do and our plan. I'm not really worried about what other people think.
"Going into a fight you never plan on stopping the guy. You hope you can. It would be a great result, but this guy has come prepared and is ready as well.
"I know this guy, I know what he brings, and the power that he presents in the ring. I think that just a win will be great but we'll see what happens. Like you saw in the fight at the weekend - one punch can change everything."
Parker was referring in particular to Joshua's uppercut in the 11th round against Klitschko which was the beginning of the end for a 41-year-old who had bounced back off the canvas in the fifth round to send Joshua crashing down in the sixth.
How Parker himself would like to finish the fight against Cojanu in such decisive fashion.
Trainer Kevin Barry was keen to stress that Parker has done that before and he no doubt will again, but the attitude among many in the boxing world is that now that Joshua is sitting atop the division, everyone else by definition is second rate.
Asked about those who doubt his power, Parker replied, with an edge in his voice: "Say what you want to say and believe what you want to believe. Is is about power or is it about speed? Can he catch me or can he not? We'll see.
"I feel like I'm in great shape mentally and physically. I feel like the changes that have come before this fight haven't really affected me because I feel like I'm ready for whatever comes my way."
Barry, meanwhile, believes Parker wouldn't have let Joshua off the hook like a tiring Klitschko did, saying: "I can promise you this; if Joseph Parker hit Anthony Joshua on the chin and had him on his back like he was in the sixth round of that fight, that fight would be over. There would be no rounds seven to 11.
"Joe has very heavy hands and uncommon hand speed for a heavyweight. Does he hit as hard as Joshua? No, I don't think he does, but when you combine Joe's power with his speed, that combination for me is as lethal as anything Joshua has."