Starring in his side's crucial win over Victoria on Thursday, Lehmann scored a highly inventive 62 not out late in the innings, in a knock which ultimately proved decisive in the Redbacks' 11-run win at North Sydney Oval.
South Australia posted an imposing 6-356 with the help of half-centuries from Jake Weatherald (71 from 51 balls) and Callum Ferguson (73 from 72).
In reply, Victoria were always marginally behind the run-rate but some late hitting had them end just shy of their target at 8-345.
Coming in at No.6, Lehmann used the full width of the crease and played a variety of ramp shots to bring up an extraordinary 50 off just 22 balls.
It was the third quickest fastest half-century in the 48-year history of the competition, bettered only by Glenn Maxwell (19 balls) and David Hookes (21).
"I really want to turn those highlights-style innings into match-winning stuff and I guess I did that today, so I just need to start more of that with the white ball," Lehmann said.
"It was a pretty good wicket with one short side. It is lucky when it (innovative batting) comes off now and then and it just went my way today.
"I haven't really done it too much before. With the fields (Victorian captain) Pete Handscomb set with no fine leg, I thought I would give it a crack, so I might have to go back to it again I reckon."
Travis Dean compiled a smart debut century for Victoria before his dismissal for 119 signalled the beginning of the end for the Bushrangers.
Cameron Valente bowled beautifully under pressure at the death, picking up figures of 3/54 which effectively ended the run-chase for Victoria.
The Redbacks moved into second with the win ahead of Sunday's final-round match-up against Western Australia.