Green’s Dictionary of Slang

1. to get the better of, to beat.

1878		J.H. Beadle Western Wilds 41: More’n once the robbers would tackle some gritty man that was handy with his ‘barkers,’ an’ he’d get away with two or three of ’em.
1905		J.W. Carr ‘Words from Northwest Arkansas’ in DN III:i 81: get away with, v. To humiliate. ‘That got away with him.’.

2. (Aus.) to strike up a relationship with, to seduce.

1880		Bulletin (Sydney) 10 Apr. 3/4: ‘You girls call your sweethearts ‘darlings,’ and you men call yours ‘daises,’ [sic] and you girls are afraid to come up here for fear some other girls will get off with your ‘darlings,’ and you men for fear some other men will get away with your ‘daisies’ .
1934		McArthur & Kingsley No Mean City 34: ‘Not many of them,’ he thought triumphantly, ‘cud get awa’ wi’ a bit of stuff like Marry Hay’.
1971		Sexy (Sydney) 2/4: [Y]ou will have your chance to tumble that bird in the office, but remember the boss also wants to get way with her [Simes:DLSS].