Starting at 11.31am, the top three elite men were out of their starting blocks in quick order, getting over to the far side of the Whanganui East section of the river, with Dunham taking the closest line to the shore.
Drysdale swiftly put a two length lead on Storey and altered his line accordingly to make the Cantabrian have to contend with a little 'dirty water' as they headed upstream.
While Storey managed to pull back half a length on Drysdale as they came to the two buoys that would make up the wide turn home this year, Drysdale only needed a quick glance ahead of him before he was powering into his signature long strokes.
Storey tried to up his tempo with quicker strokes, while first-timer Dunham needed an extra look to make sure he didn't drift into the middle of the river and have a collision with any of the lower grade rowers still coming up.
Drysdale was showing no signs that his recent 40th birthday had signalled a down turn as he powered away to the finishline, having led from start to finish, crossing the line at 11.52am with Storey and Dunham finishing wistfully behind him.
"They have absolutely outclassed and distanced this field," said commentator and former world champion Philippa Baker-Hogan.
Scheenaard gave a happy wave as she finished just under two minutes later.
Although no 5km river race is easy, Drysdale said he had felt pretty good for competition at this time of year.
"It's nice to go do it in some racing, rather than training.
"That was the best Billy Webb [I've done].
"A lot of the time I'm on a break or coming off a break."
The lack of recent fitness played a role in Drysdale missing out in 2016-17, in one case due to not racing since the Rio Olympics and the other coming after a 12 month sabbatical, but he agreed the time with Tonks had helped him get ready for this challenge, which could possibly be the last under the current format.
"It's been great. I'm proud to say I've been here every year.
"It's a great event and hopefully they find a way to keep it going."
Storey had enjoyed the conditions for racing, but not the fact that Drysdale was in condition himself.
"Beautiful weather out there, I remember two years ago we had howling wind.
"Just probably wasn't aggressive enough getting out, because when you're in front you can control the race.
"He just seemed to be sitting on my stern the whole way."
While a lightweight, Dunham had relished the chance to test himself in long course river racing, having been keen to try the challenge in 2017 until illness prevented it.
"It's just so different to what you do in a 2km race. In a 2km, you're just doing your own race."
It was the first time he had dealt with buoys and turns in competition.
"Once you're back [around], you're going to work even harder.
"I'm just so appreciative to get to take part.
"Hopefully next year they'll be even more people and it will be more chaotic."
Although she was a little worried how she would get the smaller replica Open Women's glass trophy home safely on her airplane carry-on, Scheenaard was pleased her name will be added to the original trophy "for one year".
"I heard about this race and I was on holiday with my sister and a couple of the single scullers from New Zealand invited me over."
Scheenaard had been training on Lake Karapiro with Donoghue and Loe, where they had "smashed her" in racing.
"I thought they would smash me [here] as well, but somehow I got ahead of them."
Results
Men's Open: 1. Mahe Drysdale, 21:07.72; 2. John Storey; 3. Matthew Dunham.
Women's Open: 1. Lisa Scheenaard, 23:18.26; 2. Brooke Donoghue; 3. Olivia Loe.
Men's Under 20: 1. Hugo Ver Donk, 25:38.14; 2. Jack Featherstone; 3. Jack Morris.
Women's Under 20: 1. Niamh Monk, 27:37.35; 2. Ally Bennett; 3. Cathryn Pearce.
Men's Under 17: 1. Blake Hogan, 24:17.85; 2. Leo Hanna; 3. Tim Haldane.
Women's Under 17: 1. Alice Fahey, 27:49.15; 2. Phoebe Collier.
Men's Masters Over 40: 1. Martin Bridger, 25:46.62; 2. Eric Van Donk; 3. Colin Wright.
Women's Masters Over 40: 1. Fleur Spriggs, 27:27.07.
Men's Masters Over 60: 1. Bob Evans, 27:27.77; 2. Trevor Rush; 3. Peer Nielsen.
