Sly Dai, ridden by Llinos Jones, completed the 22-mile course in a time of two hours and seven minutes.
The nearest human runner finished ten minutes behind, with a time of two hours and seventeen minutes.
The winning rider, Miss Jones, who also owns the horse, said: "It's great to have won. I'm a local girl and I've been coming to see the race since I was a little girl but this was the first time I've competed so I'm really happy.
"My horse did fantastically well. You have to be careful on a hot day like this because can overheat very quickly so you have to manage them carefully.
"But it's another victory for the horse so they're clearly still on top – for this year at least."
Miss Jones was awarded 1,000 guineas for her victory.
The 283 individual runners joined 60 relay teams of three runners each and the horses for the race.
The event starts in the town centre and is run over hilly farm tracks, footpaths, forestry roads and open moorland.
The first race took place in June 1980 and has been a regular fixture in the Welsh town, which also known for its annual Bog Snorkelling Championships.
The race was originally staged to settle a pub debate as to which is faster over a long distance.
The margins by which horses outpace their human rivals have dropped from about 30 minutes to a matter of seconds.
In 2004 Huw Lobb – who ran marathons for Team GB at the time – became the first of only two men to win the race.
Gareth Davis, the chairman of the Man v Horse event, said: “It was a very hot day, so it’s been an excellent ride by the horse, which must have been in a very good condition.
“The race goes from strength to strength every year and we get people coming in from far and wide to take part in the fun.”
ShareThis