The marque's flagship #23 NISMO machine of Ronnie Quintarelli and Tsugio Matsuda reached the magic figure in the first of four test sessions held over the course of the two days on Saturday morning, while Quintarelli was driving.
That was en route to the second-fastest time of the rain-disrupted test, as Quintarelli clocked a 1m28.139s to get within two tenths of the benchmark established by TOM'S Toyota driver Sho Tsuboi.
Four-time series champion Quintarelli said he was pleased to get confirmation that the new Z has eliminated one of the weak points of Nissan's previous GT500 model, the GT-R, whose high-downforce, high-drag philosophy made Fuji something of a weak track for the brand.
"We had a tailwind, but we reached 300km/h," Quintarelli told Motorsport.com. "I was watching the speedometer before braking… but the tailwind made it really hard to stop the car, I had to brake earlier.
"With the GT-R, usually we were around 291, 292… with these conditions, maybe 293. So we’ve definitely made an improvement.
"I was watching Tsugio when he was driving, he was doing 297, 298, and I saw two Toyotas were doing 300 and some others were at around 295, so obviously they are running with different set-ups.
"That’s a good point. When you are more than 5km/h slower in a straight line, it’s difficult."
Speaking to Motorsport.com, Nissan SUPER GT executive director Motohiro Matsumura didn't want to read too much into the Z's chart-topping speed trap figures given the conditions, but was nonetheless encouraged.
"There was a four or five-metre [per second] tailwind [14-18km/h], that’s why it’s hard to compare our car to Honda and Toyota," Matsumura said. "As far as I know, Toyota recorded almost 300km/h and Honda was about 2km/h less.
"My main satisfaction is that all four cars are around the same top speed despite running different set-ups, including ride height."
Quintarelli said last year that he hoped the new Z would allow Nissan to end its competitive "nightmare" at Fuji, which before the 2020-spec GT-R had traditionally been a strong venue for the marque.
Asked if he felt based on the evidence of winter testing whether Nissan would be able to fight for wins again at the track, the Italian said he felt that Toyota would likely still hold the edge.
"For sure, looking back at the times when we were not running together [in February private testing], Toyota were doing mid-1m26s, which is impressive," said Quintarelli. "We just hope to be as close as possible.
"I’m not sure we can say we are in front. But it’s not like the last two years, where we had no chance. To be close is a step forward."
