Vasselon, technical director of Toyota Gazoo Racing Europe, put the Japanese driver's advantage over team-mate Brendon Hartley down to his renowned qualifying pace and local knowledge of the Fuji Speedway.
"He got everything right: the timing, the tyre preparation and the way he handled the circuit," explained Vasselon.
"We have seen at Fuji drivers who are used to the circuit have a small advantage. We see it in all teams: the fast guys are those who have been racing here a lot."
Kobayashi, who is also the team principal of the TGR WEC squad, admitted that he was surprised by his 1m27.794s lap aboard the #7 Toyota GR010 HYBRID Le Mans Hypercar, which was 1.5s quicker than the mark with which he took pole for the Fuji 6 Hours this time last year.
"The car felt really strong compared with practice, it improved a lot," said the Japanese driver.
"I was not expecting a lap time like that, and I was a bit shocked when I saw it."
Vasselon also conceded that Hartley, who took pole in the #8 Toyota at the Portimao WEC round in April, ran into balance issues during the 15-minute qualifying period for the Hypercar class.
"Brendon was not super-happy with the balance," he explained.
Hartley posted 1m28.418s to complete a Toyota 1-2 in qualifying on Saturday, but he was only a couple of tenths up on the third-placed Porsche 963 LMDh qualified by Kevin Estre.
Source: Autosport