Dostal, 26, from Nebraska, had never seen the course before the 7am starting gun after arriving in town on Friday night.
But he quickly showed out as an early front runner alongside Kunaal Rajpal, 33, a doctor at Tauranga Hospital. The two made an early impression before Dostal made a decisive early break over the Tauranga Harbour Bridge.
"The course was very challenging when you go around the Mount. That was absolutely difficult. It was a very Kiwi thing to send us over so much grass to finish," Dostal said smiling.
"Nothing better than this scenery though. You know given all the challenges I am absolutely happy with my time."
Rajpal wanted a personal best time which he managed, sneaking under 2h:40m for the first time.
"This was a really good event for Tauranga. I have done quite a few marathons and this one was really well run," he said.
Walley, 27, was thrilled to win the women's race in 3:02:57, in her first attempt at the full distance from her usual half marathons.
"I would have been happy with anything under 3:05 being my first marathon, so I am pretty stoked. It feels good to be the first winner but it was a humbling experience," she said.
The marathon course began in downtown Tauranga, eased around the estuary then traversed a lap of the base track of Mauao before continuing on to the finish line in Papamoa.
Former Auckland Marathon winner and four-time New Zealand 10,000 metre champion, Aaron Pulford, won the men's half marathon in a sharp time of 1:09:10.
"It was just my second time running around the Mount. I usually avoid it as it is always quite busy," the Tauranga-based Pulford said.
"I am quite pleased to win this today as Jack Moody, who got second, is a strong runner from Auckland. I just put the hammer down in the last 10k and I used it as preparation for the Auckland Half Marathon at the end of the month."
Full results: totalsport.racetiming.co.nz
Marathon
Men
Ryan Dostal 2hr 37m 01s, Kunaal Rajpal 2:29:48, Bert Prendergast 2:43:20
Women
Jess Walley 3:02:57, Emily Kendrick 3:04:45, Maria Kroonenberg 3:25:09
Half Marathon
Men
Aaron Pulford 1:09:10, Jack Moody 1:10:25, Takehisa Fujiwara 1:14:40
Women
Katherine Morgan 1:27:22, Lesley Turner-Hall 1:31:10, Kylie Boyd 1:33:13
Half Marathon Walk
Pete Fowke 2:29:45, Anne Day 2:31:11, Julie Braybrook 2:38:16