The make-shift opener blasted a swashbuckling 253 from 225 balls on Friday as NSW built an imposing 196-run lead at stumps on day two.
Davies was dropped from the NSW Shield side before Christmas last season after averaging just 13.66 across five matches.
With Australia touring South Africa and Australia A in India, NSW coach Brad Haddin recalled the 25-year-old and promoted him up the order.
It proved a masterstroke as Davies chalked up NSW's first Sheffield Shield double-century for nine seasons.
No NSW batter has scored 200 runs in a day in a first-class match since Simon Katich in 2007-08.
Davies was unperturbed by a green-top pitch at Sydney's Cricket Central, flaying so many boundaries that it appeared to induce hand cramp.
He was ultimately caught slashing out to the deep after passing 250 and racking up 38 fours and four sixes.
Davies was well supported by Kurtis Patterson (54) and Jack Edwards (109 not out), after fellow opener Riley Kingsell (1) nicked off early on day two.Â
Will Salzmann (8), Ryan Hicks (0) and Jake Scott (7) fell in the final 20 minutes of play to left-arm Tasmanian debutant Marcus Bean (4-89), with NSW finishing the day at 6-441.
Earlier, NSW allrounder Jake Scott took the last wicket in the first four minutes of day two to bowl Tasmania out for 245 and collect a maiden five-wicket haul at first-class level.
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