This was Columb's first appearance in the cross-country series and so he was no threat to Groombridge for the title overall.
"It was a great track and pretty testing," said Motorcycling New Zealand cross-country commissioner Chris Smyth.
"It was a real thinkers' track, with lots of soft and treacherous areas on the course, and it became a battle of attrition too, with quite a few riders failing to finish thanks to their bikes either overheating, throwing a chain or running out of gas."
Tesselaar settled for overall runner-up for 2018, with Hamilton's Phil Goodwright, Stratford's Josh Hunger and Raglan's Brandon Given rounding out the top five on the day.
Saturday's result not only gave Groombridge his third consecutive national cross-country title, but it meant he collected the over-300cc four-stroke class title as well.
Given won the under-300cc four-stroke title and Napier's Mackenzie Wigg won the over-200cc two-stroke title, while Te Awamutu's Rachael Archer became the first female to win an all-gender class, claiming the under-200cc two-stroke title.
It was a double celebration for the Archer family, with Rachael's father, Kevin, winning the over-45 years' Super Veterans' title.
Stratford's Karl Roberts won the 35-44 years' Veterans' title and Thames rider Natasha Cairns topped the women's grade.
Meanwhile, Eltham's Adam Loveridge won the 90-minute junior grade race, held earlier in the day, that result allowing him to snatch the title away from the young man who had led the series at the start of Saturday morning, Napier's Bryn Codd.
The top five finishers in the junior race on Saturday were Loveridge, followed by Cambridge's Callum Paterson, Raglan's Coby Rooks, then Codd and Cambridge's Michael Henry.
Loveridge was also able to claim the over-85cc two-stroke class trophy, while Rooks won the over-200cc four-stroke title and Ngaruawahia's Luke Lempriere won the junior 85cc title.
In terms of final overall junior grade rankings, Loveridge's 2-1-7-1 score-card gave him the crown ahead of Paterson (1-20-4-2) and Codd (3-3-2-4), with Loveridge discarding his seventh placing from round three, Paterson ditching his 20th from round two and Codd dropping his fourth placing from Saturday's finale.
- Andy McGechan, www.BikesportNZ.com