Chasing 256, the Bushrangers appeared doomed until Hastings smacked 69 not out from 57 balls to steal victory at Adelaide Oval.
Victoria's triumph takes them to 23 points and they can finish no lower than second after the tournament's minor round.
SA, with 18 points and two games remaining, are favoured to take the other berth in the February 27 playoff. Queensland (15 points) and Western Australia (14 points) remain chances but both have just one match left.
But when Hussey fell in the 40th over, Victoria were still 69 runs shy of their target.
Hastings then smashed six fours and three sixes in a match-winning display which overshadowed Redback quick Richardson's superb bowling.
Richardson had not played top-line cricket since being banned from further bowling for running on the pitch during his Australian limited-overs debut last month.
But intensive remedial work on his bowling stride paid instant rewards with 5-61 from 13 overs.
The Pakistani-born tweaker took 3-47 and earned rave reviews from Australian legend Allan Border and Tom Moody, both television commentators calling for Ahmed to be considered as a late addition to Australia's tour of India.
But Ahmed, who fled Pakistan fearing for his life for supposedly promoting western values and was granted asylum last November, is ineligible for Australia until next November.
Hastings said the win was a confidence booster for the Victorians, particularly given the likelihood of meeting the Redbacks again in the final.
"To get one over them like that tonight was pretty good - pretty special," he said.
SA's Richardson had mixed feelings - disappointment at the result but relief at his successful return.
"It has been a tough three weeks ... I felt like tonight it was all good and they came out well," he said.
"To bowl 13 overs and not get a warning is a good sign so, going forward, it shouldn't be an issue."