Howick-based Marais was chasing Julian Jessop into the finish at the Eston Farmers Club when Jessop went down after colliding with a slower rider on the course, leaving the door open for Marais to grab the title.
"This means a lot to me," said the Scott/EAP Active rider. "I have been looking for this title for the last four or five years."
Marais and Jessop (PYGA Euro Steel) got away from the start fastest, with the iconic King of the Mountain prize just four kilometres into the race.
"Julian (Jessop) and I were able to sprint for it and I was able to just edge ahead of him," said Marais.
After the King of the Mountain climb the pair was joined by Andrew Hill (TIB Insurance) and they worked together for most of the race, until the leading trio inadvertently took a wrong turn, with about 15 kilometres to go.
"It was at a rough river crossing and I think we all went on last year's route instead of following the markers," said Hill. "When we realised the mistake, we all turned back together. Luckily no-one else had gone through ahead of us."
Hill, the winner of the recent Imana Wild Ride, suffered the most from the unplanned detour, as he punctured and fell off the front bunch.
After playing cat and mouse in the lead-in to the finish, Jessop got the jump on Marais and was leading going into the final few turns into the Eston Farmers Club finish.
"We saw the slow rider ahead of us and called "Track, please get out of the way". He started sprinting and as we went around the corner, he went down, and Julian slipped out as well with him," said Marais.
"I was lucky. I was able to see it and brake in time and got around both of them," he said.
"It's great to take this title, but I would have liked to win it under different circumstances," he added.
Hill bounced back from his puncture to claim third ahead of Brennan Anderson, with Leeroy Emslie holding off Sthembiso Mbatha for fifth.
In the women's race Red Bull's Bianca Haw made the women's title race her own early on, and immersed herself in a dice to race through the men's A batch ahead of her.
Bouncing back from glandular fever, Haw is building towards her Cross Country World Champs Under 23 bid in Cairns, Australia later in the year, and said she was thrilled with her form over the demanding 64 kilometre course.
"I was a little worried because there were a lot of strong girls on the startline," said Haw. "I started feeling comfortable on the climb and sprinted for the King of the Mountain, which I just managed to win."
"Tiffany (Keep) stayed with me for a while and when she dropped off I was on my own, but it was great catching the guys in A batch,' she added.
"I did blow at the end though, thinking it was 60 kays when it was actually 64," she chirped.
She coasted home unchallenged to take the title by more than ten minutes from a frantic three-way dice for second won by Tiffany Keep from Hayley Smith and veteran Nathalie Bergstrom.
The well supported 40km aQuellé Half Marathon was impressively won by Bradley Rowlett, while the signature 18km Stihl Tala 18km Family Ride took the runners and riders close to the White Rhino in the Tala Private Collection Game Reserve.
SUMMARY OF RESULTS
60km Illovo Eston MTB Marathon
1.Stuart Marais 2:30:46
2.Julian Jessop 2:30:54
3.Andrew Hill 2:32:04
4.Brennan Anderson 2:34:02
5.Leeroy Emslie 2:35:35
6.Sthembiso Masango 2:35:36
7.Bryan Powell 2:35:37
8.Jedson Tooms 2:38:23
9.Wayde Finch 2:38:33
60km Illovo Eston MTB Marathon - Women
1.Bianca Haw 2:51:27
2.Tiffany Keep 3:03:06
3.Hayley Smith 3:03:06
4.Nathalie Bergstrom 3:03:08
5.Christie-Leigh Hearder 3:10:16
aQuellé 40km Half Marathon
1.Bradley Rowlett 1:41:50
2.Travis Stedman 1:44:23
3.Kusaselihle Ngidi 1:45:33
4.Njabulo Cele 1:45:35
5.Dean Worthmann 1:45:51
More information can be found at www.illovoestonmtb.co.za