The New Zealander fired earlier rounds of 67-66 to set up another opportunity to claim a major amateur title and a place at next year's Masters Tournament.
Cameron Smith is the best of the Australians at 10-under-par following rounds of 68-69-69 to be in 3rd position and to be in with a chance to take this title.
The third round belong to the defending champion Matsuyama.
The 19-year-old from Tohoku Fukushi University has become something of a Saturday specialist. Last year in this event he shot 65 on the Saturday and also shot a third round 67 at this year's Masters Tournament on his way to winning the Silver Cup for low amateur.
Seven birdies in a bogey free round saw the Japanese star light up the tournament after a day that began with severe weather delays.
The delays didn't seem to bother Campbell and birdie on the par 5 18th at The Singapore Island Country Club made amends for the double bogey on the 12 to give the world number 17 a stroke buffer heading into the final round.
"I finished birdie, par, birdie, so that wasn't too bad," remarked Campbell after the round.
"I had a disappointing double when I was at 14 under, so it would have been nice to keep my low round going, but we'll see what happens tomorrow."
Understandably the media attention is focused upon Matsuyama. The Japanese press has that type of style of swamping their players and saturating the news with their young guns.
That's probably not a bad thing for Campbell as he's a player that can zone in to the task at hand, irrespective of the surrounding distractions.
"I just like to play my own game and focus on that. I don't want to pay attention to what anyone else is doing on the course. I try to shoot the best that I can, if it is good enough it is good enough, and if it's not then it's not."
Cameron Smith's closing 69 was also impressive to place him within the hunt for this title.
All week Smith has played stellar golf carding fourteen birdies, thirty-six pars and recording just four bogeys in his three rounds. With a world ranking of 30 and closing, the Australian Amateur Medal champion continues to stake his claim on the main amateur stage after an impressive junior career.
I would not be surprise to see Smith scorch The Singapore Island Country Club layout during Sunday's final round and being paired with Campbell and Matsuyama will enable Smith to apply the pressure when needed.
As for the remaining Australians, Matt Stieger is in a tie for 9th position following rounds of 70-72-69 to be at 5-under-par, Jake Higginbottom is a stroke behind at 4-under-par and Luke Humphries is currently in 23rd position at 1-over-par.
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