NEW YORK - A Picasso portrait of his mistress Dora Maar, called Femme Assise, Robe Bleue (Seated Woman in Blue Dress), painted on the Spanish master's 58th birthday, sold for $45 million at Christie's art sale on Monday, kicking off a week of high-profile auctions expected to rake in hundreds of millions of dollars.

Christie's and Sotheby's - esteemed houses founded in 18th-century London - are chasing combined sales of at least $1.1 billion in offering hundreds of contemporary, modern and impressionist works for auction in New York.

The Picasso portrait was only the second most expensive lot of the Christie's auction. A bronze of a woman's head, La Muse Endormie (The Sleeping Muse), sold for $57.37 million, a new auction record for Romanian-born sculptor Constantin Brancusi and fetching over twice its lowest pre-sale estimate, Christie's said.

The Picasso oil portrait, which had been valued presale at $35 million to $50 million, was originally owned by the artist's friend and gallerist Paul Rosenberg, before being confiscated by the Nazis and recovered by Free French Forces. It was later acquired by US financier and industrialist George David Thompson.

The top estimate for the week is a 1982 Untitled by Jean-Michel Basquiat - a skull-like head on a giant canvas in oil-stick, acrylic and spray paint - for which Sotheby's hopes to smash a new auction record for the US artist at more than $60 million.

Much of the art being offered this season is fresh to market - 84 percent of the works offered by Christie's on Monday had never been offered at auction or have been off the market for 20 years or more.

Christie's said the evening sale, including works by Monet, Chagall and Fernand Leger, fetched $289 million.

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