But all the top challengers were in that group, meaning there was no change in the standings as Froome maintained his 12sec lead over compatriot and Sky team-mate Geraint Thomas and 14sec to Aru.
They will be further tested on Sunday, when the ninth stage takes the peloton through the Jura mountains with three lung-busting climbs in prospect before a risky descent to Chambery.
By now, LottoNL-Jumbo's Robert Gesink was his closest pursuer, going over the top of the climb around 20 seconds later, but would finish 37 seconds behind the French rider.
Tour leader Chris Froome finished in a group further back, retaining the yellow jersey ahead of a second, far harder day of climbing, again in the Jura mountains, on Sunday.
It was the second win at this Tour for a French rider, after Arnaud Demare's on Stage 4.
Calmejane, the 24-year-old from the French wildcard Direct Energie team, showed maturity beyond his years to solo to a magnificent win in a compelling 187.5km stage from Dole to Station des Rousses - snaring the polka dot jersey in the process.
Team Sky race leader Chris Froome said: "Today some teams wanted the [race leader's] yellow jersey... we couldn't let them go".
Thomas crashed but he was quickly back on his bike.
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Cramps threatened to derail Calmejane's charge to the line, with the grimacing youngster nearly coming to a complete standstill on an uphill drag in the final 6km.
But Calmejane, a stage victor at last year's Vuelta, countered and passed them, cresting the summit first and guanteeing himself the polka dot jersey by one point from Astana's Fabio Aru.
The Team Sky-led peloton mopped up the remnants of the breakaway as Guillaume Martin took third at 50sec.
Calmejane's team is one of 22 Pro-Continental outfits - effectively the second division of professional cycling.
Calmejane's victory was his fourth of the season and came 10 months after he capped his debut Vuelta a Espana with a similarly fantastic stage win over similarly undulating terrain.
"That was a tough day", he said.
That's the monstrous challenge lurking on Sunday for the 193 already exhausted and sunbaked riders who have made it this far.
An ascent of the Mont du Chat comes late in the 181.5km route from Nantua to Chambery, which includes as many of seven climbs in all and could have a huge say in how the Tour pans out. "I imagine it's going to blow the general classification right open".