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'Femme assise pres d'une fenetre' (A woman sitting by a window) by Spanish artist Pablo Picasso, sold for $45 million at Sotheby's auction house in central London.

LONDON -- A Pablo Picasso portrait of his mistress and "golden muse" Marie-Therese Walter sold for $45 million on Tuesday, leading an important Sotheby's auction of impressionist, modern and surrealist art.

The sale was the first of a series held in London this month by Sotheby's, Christie's and smaller auction houses in the latest barometer of the strength of the high-end art market.

Prices for the most sought-after works have soared in recent years despite broader economic concerns, with collectors in China, Russia and the Middle East joining more established patrons in Europe and the United States.

Subtracting the buyer's premium of more than 10 percent, the amount realized for the 1932 Picasso was at the lower end of pre-sale estimates of $39 million-$55 million.

Nonetheless, it was comfortably the top lot of an evening when a series of works on paper by Austrian artist Egon Schiele arguably stole the limelight.

Schiele's 1914 "Lovers (Self Portrait With Wally)" fetched $12 million, an auction record for the artist for a work on paper.

Also sold by the Leopold Museum in Vienna was his "Self Portrait in Green Shirt with Eyes Closed" which sold for $8 million, well above expectations of between $3 million and $4 million.

The combined tally for Schiele works, sold by the museum to help settle a long-running restitution case involving art deemed to have been stolen by the Nazis in the 1930s, was $22 million.

'Strongest offering in many years'
Other lots fared less well, notably Max Beckmann's "Before the Ball - Two Women With a Cat" which went unsold despite pre-sale estimates of $8 million-$13 million.

Overall the evening brought in $189.4 in sales, within expectations of $161 million-$233 million. Sotheby's said it was their second highest total from an equivalent sale in London.

"Bidders, both new to the market as well as seasoned buyers, reacted with great enthusiasm, in particular to the selection of impressionist works that were considered to be the strongest offering in many years," said Helena Newman, chair of Sotheby's impressionist and modern art in Europe.

Christie's, the world's largest auction house, holds its sale in London on Wednesday.

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