The 36-year-old veteran started the race at breakneck speed, took a big lead early on, but fell behind at the end.
It went a little too fast. I feel like there's not much to gain on the second lap. But I think I'm holding on and holding it together well anyway, said Halfvarsson in Viaplay's television broadcast.
"Goes black before the eyes"
Starting at a high pace was a conscious tactic, simply to show off before the Olympic selection.
"Yes, I have to do it. I have to show what I stand for. You can't back down, even if it goes black at the end. I'm really happy," he said.
The Swede finished sixth, 24 seconds behind the winner, Martin Løwstrøm Nyenget, from Norway.
The day was the best Swedish day on the men's side this season, with three Swedes in the top 15. Johan Häggström was the second-best Swede in 12th place, and Leo Johansson came in 14th.
Finland's Iivo Niskanen and Norwegian Erik Valnes took the other podium places in the race.
"Very proud"
The race in Oberhof on Sunday was Halfvarsson's first World Cup competition this season after a few chaotic months with a lot of illness.
"I have a miserable background. I don't know how I manage to put this together. I'm very proud of myself," he said.
Now the question is whether the effort is enough to be selected for the Olympics in Milano-Cortina in February.
"I'm not the one who selects any Olympic team. We'll see if this is enough," said Halfvarsson.
The final selection will be made on Tuesday, January 20th.
