The former White Hills left-hander made a career-best 223 off just 158 balls, including 21 fours and nine sixes, against South Hobart Sandy Bay in Launceston.

Playing in Tassie until the Victorian Premier Cricket season begins on November 28, Stepien was involved in a 368-run stand for the third wicket with his Greater Northern and Carlton team-mate Evan Gulbis, who finished 226 not out in his side's stunning score of 4-504 declared off 74 overs.

Stepien and Gulbis' stand set a new league record for the third wicket and was the fourth-highest partnership in league history for any wicket.

Stepien looked set to make 300 in a day before he was trapped lbw for 223.

There were still 43 overs remaining in the day's play when Stepien walked off the ground to a standing ovation from his team-mates and Greater Northern supporters.

After opening the batting, Stepien made 97 off 97 balls in the first session before lunch.

His first three deliveries after lunch were dot balls before he launched a six over mid-wicket to bring up his century.

Then he went up a gear. From 103 off 101 balls, Stepien proceeded to smash 120 off his next 57 balls.

His double-century came via a boundary in the 50th over of play and then he raced from 201 to 223 in the space of one over thanks largely to three consecutive sixes off the bowling of Caedence Kuepper (0-84 off eight overs).

"It was just nice to get amongst the runs,'' Stepien said.

"It was nice to get to 100 and then Evan told me to make sure I turned it into a big one.

"When I got to about 160. Evan said to me 'mate, there's not many moments when you're 160 not out on a good wicket, make the most of this opportunity'.

"It was good to go on and get a big score. Once you get past that 100 stage the pressure does release a bit.

"You feel as though you're hitting the ball well and playing proper cricket shots.

"I felt like I was hitting the ball well and I just tried to keep executing."

Stepien said the possibility of making 300 in a day never entered his mind.

"We just wanted to focus on what we were doing rather than thinking about what we were going to make,'' he said.

"We had plans to execute against their quicks and we had plans to execute against their spinners.

"We executed those plans really well."

Gulbis didn't slow down once Stepien departed.

The star all-rounder finished 226 not out off 199 balls when the declaration was called.

Stepien said it was a special moment to share the innings with Gulbis.

"Evan's been my mentor for the past four years at Carlton, so to have him at the other end to share that moment was pretty special,'' he said.

"I'm really grateful for what he's done for me.

"You don't play cricket to set records, you play cricket with your mates and to have fun, but it's a nice accolade to have."

At stumps on day one, South Hobart Sandy Bay were 1-41.

Have you signed up to the Bendigo Advertiser's daily newsletter and breaking news emails? You can register below and make sure you are up to date with everything that's happening in central Victoria.