The 37-year-old Dunedin runner, who is the surveys manager at the University of Otago, cleaned up the field to win the event in 2hr 39min 11sec.
It was quite an achievement considering he had just 2½ months to train for it. He broke his clavicle after slipping while running down from Flagstaff summit in December last year.
A long recovery was lengthened when he initially tried to train while the bone healed.
Despite that, he felt good in perfect conditions in Southland on Sunday as he shot out to an early lead and pushed through to get within a minute of his personal-best time.
''[Preparation] was a bit of a struggle this year,'' Mirosa said.
''I felt like I was really underdone for that race. I would usually prepare a lot more for a marathon, but I thought since I hadn't been racing a lot this year I would just get something under my belt to see where I was standing.
''But I guess the good thing was that I was well rested and I wasn't dealing with any injuries or anything, which is often the case when I'm training quite hard.''
He often struggled with niggles to his achilles and knee, which hampered his preparations for last year's Dunedin Marathon, an event he also won.
The marathon, from Riverton to Invercargill, is in its 107th year and is the oldest in the southern hemisphere. When he took up marathon running in 2012 it was the first event Mirosa ran in, when he finished second in 2hr 44min 53sec.
''It's not that I've done hundreds of marathons. I think I'm up to nine now, but that was my first marathon when I started running them. So I felt quite good about doing a good time there and also winning. That was quite significant for me personally.
''There wasn't a lot of competition which was a bit of a shame, so I had to push through by myself.
''I don't mind it so much because I train by myself most of the time, but for the marathon I guess it's a shame there's not more competitive runners doing it, or just runners in general.
''In terms of its history, it's quite a major marathon, so I just felt it would be good if more people were making the effort to come down and celebrate that.''
It would be Mirosa's last run in New Zealand for a while, as he was set to travel to Taiwan and Beijing with his family. He would spend a month in each location as his wife, an academic at the University of Otago, did some work for the Ministry of Primary Industries.
He hoped to do some running while away and then thought he may try a trail marathon, such as the Motatapu, when he returned.
