When the boy lost the game, Gray stripped off the boy's underwear as well as his own.
He then briefly performed a sexual act on him.
Gray then drove the boy home, where he drank beer with the victim's father.
It was only after Gray left that the boy was able to tell his father what happened.
When police searched Gray's home they seized a computer, hard drive and writeable CDs which were found to contain more than 4400 images and videos of children performing sexual acts or being sexually abused - some of them as young as two.
Defence lawyer Jock Blathwayt said his client had not acted violently and the offending itself was only brief.
His client appreciated the serious consequences of what he had done and had sought help for his addiction to pornography, which he accepted was a "serious problem".
Gray had lost his job and his status as a leader of a sports club, and his offending had "deeply distressed and depressed" his partner, who remained with him.
Judge Susan Thomas read aloud from victim impact statements from the boy's parents.
The victim's father said he had trusted Gray with his children and thought he was a "genuine person who wouldn't hurt a fly".
He had since felt an intense rage, betrayal and sadness at what had happened. He could no longer work properly, had lost his clients and eventually had to give up his business.
In her victim impact statement, the boy's mother said one word described her son - "innocent".
"But what you took away from him was that and so much more."
She said her son had been a cheeky, sweet, fun-loving child but now he was quick to anger.
The family had sunk into a dark hole and "a large grey cloud" now hung over them.
She felt disgust that her son had called Gray "uncle" and felt guilty for what had happened.
Judge Thomas said Gray's age compared with his victim's was an aggravating factor, as was the premeditation and breach of trust of the offending.
"How many 41-year-old's play strip poker with a 10-year-old child?"
She said Gray's victim might not fully appreciate what had happened until he was older and the breach of trust was felt more deeply.
Judge Thomas sentenced Gray to two and a half years in prison for all the charges - the first two of which were first-strike offences.
She also ordered Gray pay $3000 to his victim in reparation for emotional harm, which Gray had offered to do.
