"Over a couple of rounds I managed to beat him by one point, but as [the general knowledge questions] were so New Zealand skewed I thought that was a little unfair," McDouall said.
"He did very well on his specialist subject which was American history, but that was obviously left on the cutting room floor."
McDouall was asked questions about the longest-serving New Zealand prime minister and which film set Matamata was closest to, correctly answering Richard Seddon and Hobbiton.
Wallace was asked questions such as who launched The Humanity Star and what Clarke Gayford's TV show was about.
He incorrectly answered Houston and interior decorating. The correct answers were Rocket Lab and fishing.
McDouall said Wallace, who is travelling New Zealand promoting his book Chasing the Dream, was extremely sharp and a classy character.
"He asked me some stuff about my specialist subject and what was amazing is after I said it was David Bowie he just spouted about 10 facts about him," McDouall said.
"It was like 'wow, this guy must walk around with a drop-down menu in his head'. It was absolutely phenomenal."
The two have a lot more in common than just their quizzing backgrounds; they enjoyed talking about football, London and law as both are qualified lawyers.
When interviewed on the show by Hilary Barry and Wells, Wallace said getting called to the bar would always be the proudest moment of his life.
"... as an 11-year-old boy, I was like the Muhammad Ali of my class, 'I'm going to be a lawyer' and I talked the talk and I managed to walk the walk," Wallace said.
Wallace was called to the bar in 1984, he won Mastermind in 2004 and has been appearing on popular TV quiz show The Chase since 2009.
McDouall said his children enjoyed the show, but he had limited opportunities to catch it as he was rarely home before six.
"Every so often when I go around to my mums it'll be on and I'll watch it. Shaun's certainly impressed me then.
"I think Sinnerman would be impossible to beat, he is so incredibly learned."
McDouall won TVNZ's Mastermind in 1990. His specialist subject was the life and works of David Bowie. He also won Sale of the Century the year before that.
He still enjoys going to pub quizzes with his son, if the atmosphere is family friendly and would relish the opportunity to battle Wallace again, next time at a Mastermind level.