Ms Murphy entered him in the competition last year and chose his clothes, spending hours working on his hat.
But he missed the heats and couldn't take part.
"And she was bitterly disappointed. So this year, that's the reason I entered," Mr Green told the Herald.
With the help of a close friend, he put together a clothing design and yesterday "came away with the result".
"The whole thing was done in her memory. She's an amazingly beautiful woman ... and so loving and caring and intelligent. She was the perfect woman for me and I loved her dearly. To win this best-dressed competition in her honour was just absolutely a dream come true."
"I'm immensely proud."
Mr Green and Ms Murphy had been planning to marry when she died.
"I knew that she was the girl for me from the day I took her out on the first date."
He was able to stay composed amid the emotion yesterday, but said grief hit him at different times.
"But there are some things to be thankful for. I had three and a quarter years with the most beautiful woman in the world."
About 22,000 people were at Addington Raceway in a mixture of sunshine and rain to see the racing that culminated in the NZ Trotting Cup.
The crowd included several All Blacks - with the William Webb Ellis Cup - and Prime Minister John Key.
Mr Key said: "It's just one of those things that Cantabrians look forward to anyway. But with the earthquakes and all the pressures and strains that have been on Christchurch, it's nice to come out and forget about it all and just have a day at the races, and dress up and have a couple of drinks and have a bit of fun."
The day was made even better for Christchurch when Mr Key announced the Crusaders would have a new home in the form of a $20 million sports stadium that will replace quake-damaged AMI Stadium.
The cost of the temporary stadium, at Rugby League Park, next to Addington Raceway, will be picked up by the Government, with help from the Christchurch City Council and New Zealand Rugby Union.
It will also enable Christchurch to host an All Blacks test against Ireland in June.