The composite four of Boyd, fellow Blackjack and sister Angela, along with Leigh Griffin and Sheryl McLean, got away to a confident start against the Sandra Keith-skipped four in the final, drawing two shots on the first of the 18-end encounter.
But it was Keith and her team of fellow Blackjacks Amy McIlroy, Serena Matthews and Selina Goddard who were quick to respond by opening up a five-shot lead after four ends.
Drawing four shots on the fifth end and adding another for good measure on the sixth, Boyd had the game tied up at 7-7.
Her team then did a superb job in countering the attacking qualities of the Keith quartet, with superb draw play and defence of shot bowls.
Such was the intensity that after the allotted 18 ends of play the scores were locked at 15-15, forcing an extra end to decide the champion, after Boyd opted for a safety-first option in not playing her last bowl.
A Keith team bowl was neatly perched alongside the jack and one of her team bowls was against the shot bowl.
Any movement of the head could have proved fatal for Boyd and handed Keith the title.
The extra end was an intense affair and required several deliberations within each team, particularly when the skips stepped up to play their two bowls.
With the Boyd four holding shot Keith attempted to draw only to miss shot by the narrowest of margins.
Keith then successfully plugged the gap in the line Keith's bowl travelled, forcing her to tighten her line of fire.
Keith did so but narrowly missed again and the Boyd team all sounding a huge sigh of relief.
It was Mandy Boyd's fourth national fours title, to go with two national singles titles.
``It was a really close game,'' Mandy said.
``It took us a while to find the speed of it [green], but it was the same for both teams.
`` It took a wee minute to really tighten it up. It was end for end and this showed through with the need for an extra end.''
Boyd added that with the experience in Keith's team, she know it was always going to be ``a really tough game''.
This year's fours title was Angela Boyd's fifth national title, entitling her to a gold star award.
For Griffin the title is the fifth consecutive national title won by players from Wellington's Victoria Bowling Club, with Helen King winning the singles title in 2014, Griffin the singles title in 2015 and fours title in 2016, and Neville Rodda winning the pairs title last year with Gary Lawson.
Jo Edwards won the award for most constant player in women's competition during the 12-day tournament.
``It's always a bonus,'' the newly crowned national women's singles champion said of being recognised with the award.
``You don't go looking for these things, but when they come along it's pretty cool.''
All up Edwards was pleased with how she and long-time pairs and fours team-mate Val Smith tracked during the tournament.
