(Adds share price, reaction)
By Kate Holton
LONDON, March 4 (Reuters) - WPP outperformed globaladvertising rivals Omnicom and Publicis by winning big accountsin 2015, beating sales forecasts and saying it had made a solidstart to 2016 despite some difficult markets.
The world's largest ad group said on Friday strong demand inNorth America, Britain and the big markets of Europe helped itpost its best growth of the year in the fourth quarter, and makea solid start to 2016.
New account wins from companies such as Unilever, L'Orealand Tesco helped WPP to secure 5.6 billion pounds ($7.9 billion)worth of net new business in the year, putting it at the top ofthe league table for new work for the fourth year in a row.
"We see WPP as the best positioned of the agencies group,"said analysts at Liberum, noting the broad geographicalfootprint and the fact Publicis has struggled since it withdrewfrom a planned merger with Omnicom in 2014.
The Ogilvy & Mather and JWT owner echoed U.S. group Omnicom and French ad agency Publicis with a solid endto 2015.
Although analysts welcomed the results, noting cost controlshad helped lift operating margins, its shares gave up earlytrading gains and were down 0.5 percent at 0930 GMT, with somenoting that the outlook remained cautious.
While events such as the Rio Olympics and U.S. Presidentialelection should boost sales, low oil prices, global economicuncertainty and the potential that Britain could leave theEuropean Union in a June referendum were all likely to temperclients' willingness to spend big on advertising.
WPP reported fourth-quarter like-for-like net sales growthof 4.9 percent, the strongest quarter of the year, giving it afull-year figure of 3.3 percent, slightly ahead of forecasts.
The group said it expected to produce a similar net salesgrowth rate for 2016 with an improvement in profitability andsaid it had already enjoyed an above-budget month in January.
The strong pace means WPP has continued to keep the pressureup on its biggest rivals due to its broad geographical spreadand its strong growth in digital sales.
Chief Executive Martin Sorrell said that while Brazil, Chinaand Russia were currently challenging, markets such as India andIndonesia were performing well.
WPP was one of the first ad groups to target emergingmarkets such as China and it now has a target of making 40-45percent of sales from digital media and faster growing nationsover the next five years. ($1 = 0.7076 pounds) (Editing by Paul Sandle and Alexander Smith)