The Belgian spoiler claimed what he called the best win of his career as top seed Coria saved two match points before crashing out.
The Argentine, sixth in the chase to China for the eight-man Masters Cup starting November 13, would have needed a semi-final showing in Switzerland to add to his possibilities of reaching the wrap-up event.
His last chance - and that of his handful of rivals - will come next week at the Paris Masters, concluding event of the ATP regular season.
Vliegen, ranked 131, said he is hitting form at just the right time after suffering a shoulder injury during practise for qualifying at Wimbledon and playing his best this season on clay.
"I'm 23 and I've been playing the big events for three years now," said the 2003 finalist at Adelaide, the match he considers the most prestigious of his career.
"But I'd be lying if I said there were no nerves in this match. You don't get many chances against Top ten players. I was lucky that I got mine and was able to take it."
The Belgian, a good friend of Kim Clijsters who was guessing that one of his post-victory text messages was coming from his compatriot, has been confined mainly to the Challenger circuit this season as he rebuilds his ranking.
"But this year, I've been able to score results consistently, instead of having a good week here and there."