The difference came with a stunning keirin victory which gave Kenny his ninth Olympic medal and his seventh gold, both British records, 13 years after he won his first in Beijing.
Many arrived at the velodrome expecting to see Laura Kenny win what would have been her sixth Olympic title, but though a crash scuppered her chances in the omnium, Jason ensured there would be family celebrations – and a 12th gold medal for the clock they have been planning to make.
The 33-year-old had complained of being out of form as he finished eighth in the men’s sprint on Thursday, handing over a second Olympic crown in the space of three days, but there was no sign of that on Sunday as he won by a yawning gap of 0.763 seconds from Azizulhasni Awang of Malaysia.
“Seven gold medals is really special, when you look back on the ones you have already got it seems pretty easy,” said Kenny. “Then when you try and get more, you remember how hard it is.
“Before today I had all but given up, I was counting my career in days and races as opposed to years, but maybe I have bought myself more time now.”
Perhaps, judging from how they rode, Kenny’s rivals in Sunday’s final thought he was finished too.
Izu is the home of Japan’s keirin school, but in all the countless sessions in this velodrome, it will rarely have seen one raced like this.
With Kenny drawn to ride first in line, Australia’s Matthew Glaetzer looked more concerned by those behind him, constantly checking over his shoulder as a gap to Kenny grew.
It was already a few bike lengths before the derny even pulled off, with Kenny scarcely able to believe it himself. Within half a lap he committed to going long, and did not look back.
“I looked and thought, it’s too big an opportunity not to try, so I just launched it and rolled the dice,” said Kenny.
“I didn’t really feel like one of the favourites, I wouldn’t have been betting on myself personally.
“I think in that incidence you have got to be ready to take your chances. A massive chance came along.”
It was a chance that had increasingly looked like eluding Kenny as he struggled for form all week, helping Jack Carlin and Ryan Owens take team sprint silver but struggling individually.
Kenny had walked away from cycling after Rio, never announcing he had retired until he reversed the decision in late 2017.
It has proven a long road back to the top. Kenny admitted he has not been able to squat properly for more than a year, while he must still work out why his speed has been missing this week, having needed a repechage to get out of the first round of this competition. But on Sunday afternoon at least, that did not matter.
“It is special to get a gold medal at the end of the day,” he said. “Just for keeping on turning up and racing hard.”
There would be no such rewards for Laura, however, as a crash ruined her omnium before the opening scratch race was over. Though the two-time defending champion recovered to win the following tempo race, a surprise early exit from the elimination event effectively signalled her medal hopes were over.
“It was a mountain to climb from that point and to be honest the tempo race I just rode off adrenaline,” she said.
“By the time the elimination race came round I was done. I was sat in the chair and I was thinking: ‘I feel sick, my back is killing me’.”
Four years after becoming a mother, Laura leaves Izu with a fifth career gold plus a silver medal – and a role as flagbearer for the closing ceremony – and has no thoughts of hanging up the bike, though she did say she might want to take a step back from the team pursuit come Paris.
“Is a bunch race specialist going to be a thing? I don’t know,” she said. “I didn’t enjoy the team pursuit as much whether now we can rebuild it and start again...”