A portrait of Treasure Island author Robert Louis Stevenson, which the writer called "too eccentric to be exhibited", has sold for $8.8m (£5m).
US painter John Singer Sargent's portrait shows the Scottish author striding across a room twirling his moustache as his wife sits behind him.
It exceeded its $7m (£3.95m) estimated price at Sotheby's in New York.
Sargent's Venetian Loggia, a scene of women in an arcade, sold for $5.6m (£3.2m) at the Wednesday auction.
The 1885 oil painting of Stevenson was bought by casino owner Steve Wynn, for inclusion in the art collection at his Las Vegas Resort and Country Club.
It follows his purchase of a Cezanne and a Renoir for a total of $40.9m (£23m) last year.
Sargent's picture was in contrast to the formal portraits of its time.
Stevenson wrote of it: "It is, I think, excellent, but is too eccentric to be exhibited."
A watercolour by Sargent entitled Madame Roger-Jourdain, depicting Sargent's Parisian friend and neighbour lying on grass, fetched $2.7m (£1.5m) at the Sotheby's auction.