Following a 78-minute delay due to a thunderstorm, Matsuyama fired an eagle and four birdies to cover the back nine at Augusta National in just 30 shots and take a massive step towards his first major title.
Aided by a hole-in-one on the sixth, Canada's Corey Conners is five shots off the lead on six under, with 2015 champion Jordan Spieth another stroke back following a 72.
Tweet of the day
Hideki Matsuyama revealed what "inspired" his back nine of 30 following the weather delay.
Quote of the day
Former champion Patrick Reed reveals he is not as impressed as some with Augusta National's famous azaleas.
Shot of the day
Corey Conners made just the sixth hole-in-one on the sixth hole in Masters history.
Worst shot of the day
Justin Thomas was still in contention when he stood over an 80-yard pitch to the 13th, but dumped his ball into Rae's Creek and ran up a triple-bogey eight.
Round of the day
Hideki Matsuyama returned from the rain delay in inspired form and came home in 30 for a brilliant 65.
Statistic of the day
Bad news for anyone hoping to make a final-day charge.
The par-five eighth to an average of just 4.389, yielding two eagles, 29 birdies and not a single bogey.
The seventh hole played to an average of 4.556, with just two players making birdie as it played to a total of 30 over par.
A cold front will move through near midday on Sunday, keeping a chance of a few showers in the forecast before 2pm before the sunshine and dry weather returns for the rest of the day. Any thunderstorms are expected to remain south and east of Augusta. Southwest winds turn west for the final round at 10-15 mph with some higher gusts during the afternoon hours.
Key tee times (all BST)
1910 Jordan Spieth, Brian Harman
1920 Will Zalatoris, Corey Conners
1930 Marc Leishman, Justin Rose
1940 Hideki Matsuyama, Xander Schauffele