But word came through about three hours after the race had ended that a decision had actually gone against him.
According to the Audi website: "Technical stewards had noted a mismatch between part numbers in the technical passport and the car.
"The exclusion from the classification was made even though the parts are identical and all fully correspond to homologation."
"Daniel [Abt] drove fantastically on both days and absolutely deserves this victory," said Allan McNish, team principal of Team Audi Sport ABT Schaeffler.
"What we are apparently suspected of is a administrative mistake in the car's passport that didn't give us any advantage at all.
"We want the opportunity to be able to clarify all details, that's why we've announced the intent to appeal."
The appeal was sent to FIA's international tribunal in Paris.
"Heartbroken," Abt wrote on Twitter. "I'm struggling to find words for this. All I know is that I did my best to make you proud. We intend to appeal the decision."
Earlier, Abt's first reaction, heard over radio while he was still in the car, was almost unprintable – but we feel obliged to share.
"F****** hell!" he said.
He'd left the Central Harbourfront track vowing to dive headlong into double celebrations when the officals' decision came down.
The decision elevated Rosenqvist to first, Montara to second and lifted Kiwi Mitch Evans (Panasonic Jaguar Racing) to third – his first Formula E podium finish.
The 26-year-old Rosenqvist had started from pole position and had fairly flown away from the field, after drivers had spent one lap behind a safety car, called out after problems with the starting lights.
But the Swede braked too hard into turn two and slipped back to 11th, allowing Formula E rookie Montara the chance to make his move.
He looked like making the race his own, too, until coming to grief on lap 43, locking up and letting Abt and Rosenqvist through.
At the line then it was Abt-Rosenqvist-Mortara. Or so everyone thought, until the late bombshell was dropped and the appeal lodged. The decision remains pending.
We could then reflect with irony over one of Abt's reactions to what he thought was his maiden victory in the electric racing season.
"That's the thing about Formula E," said Abt. "You never know who's going to win."
For so long yesterday it looked like being Mortara, the 30-year-old driver known hereabouts as Mr Macau, thanks to six wins across the pond at that city's annual Grand Prix extravaganza, in both the Formula Three (two) and GT (four) events.
Mortara had the race in his pocket until his mistake, and had looked inconsolable afterwards. Glory was within reach, but then the nuances of electric races plucked his prize away.
But Mortara fronted up in the post-race press conference, and looked to the future after such an impressive effort (otherwise) on debut.
"It's difficult to find words after a race like that," said Mortara. "We had the pace, we were managing the race. I wanted it too much and made a big mistake."
It was a day of high drama and in terms of pure entertainment, Formula E again duly delivered.
So close is the competition that there were eight teams represented in the first 10 placings – and last year's champion Lucas di Grassi left town without managing to pick a point across the weekend.
The sport's future in Hong Kong looks assured, too, after the announcement following the action that mainland private equity YF Capital – run by entrepreneurs David Yu and Jack Ma, owner of the South China Morning Post – had thrown its considerable financial clout behind the series' main Chinese partner Enova.
The official figure for the attendance across the two days was put down at around 27,000, not capacity (30,000) but enough to have Alan Fang, chief executive of Formula Electric Hong Kong Racing, looking to the future as well.
Discussions were already underway with both Formula E and the Hong Kong Government, he said.
