The German rider for Bora-Hansgrohe was strongest on the summit finish and added a Vuelta triumph to stage wins in the 2020 Tour de France and 2022 Giro d'Italia.
Bad conditions at the end of the race led organisers to take general classification times 2.05 kilometres from the finish, and Primoz Roglic burst through, snatching a couple of seconds on reigning champion Remco Evenepoel and teammate Jonas Vingegaard.
Belgian rider Evenepoel could not stay with him, meaning it was a good end to the first full week of the race for Slovenian Roglic, who won stage eight on Saturday.
His Jumbo-Visma team enjoyed a super Saturday with the three-time Vuelta winner's victory, while Sepp Kuss took the red jersey, and the American held on to it on Sunday in a wind-battered run.
"It was a nervous day, super windy, but I came through really well," said Kuss.
"It was really slippery and really muddy, so I think they made a good decision (to take early times)."
The Dutch team set the pace at the start of stage nine, 184.5 kilometres between Cartagena and Collado de la Cruz, breaking away with seven of their eight riders while Soudal-QuickStep's Evenepoel and a few others stuck with them.
The peloton caught them before a new attack sprang, not featuring any of the main general classification contenders.
The break, featuring Kamna, created a gap which at one point stretched over eight minutes on the peloton, which split in a wind-hit section.
Lenny Martinez and Wout Poels, who started the stage in the general classification top ten, were caught in the back split, behind over 20 riders in the front split.
Eventually the chase group caught up and the peloton reformed with around 50 kilometres to go, reeling in the break to around four minutes.
However they refused to be caught and swelled the gap to over five minutes entering the final 15 kilometres, approaching the category two summit finish of Alto Caravaca de la Cruz.
Kamna kicked on with Matteo Sobrero in pursuit, dropping the rest of the break, but the German held him off with ease.
"I'm super happy about it, I've worked really hard the last couple of months," said Kamna.
"I tried to make it through the echelons as quick as possible without spending too much energy.
"At the end it was tricky with the climb always going up and down."
Monday is a rest day, with the race resuming on Tuesday for stage 10, a 25-kilometre individual time trial in Valladolid.
This is the 78th edition of the Vuelta, which ends in Madrid on September 17th after 21 stages and 3,153.8 kilometres.
