UPDATE 1-WPP extends TNS offer, has 61 pct acceptance

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LONDON, Oct 3 (Reuters) - Martin Sorrell's WPP Group WPP.L moved closer to a takeover of market research firm Taylor Nelson Sofres TNS.L on Friday, securing support from 61 percent of investors and extending its offer.

WPP, the world’s second-largest advertising and marketing group, said in a statement it had extended its offer to Oct. 8, in its 1.14 billion pounds ($2.02 billion) bid battle for TNS.

WPP said on Thursday the offer was final and would not be raised. It also said on Friday it had changed the acceptance condition of the offer from 90 percent to 75 percent.

WPP first approached the British firm in May but was rebuffed as TNS explored merger talks with German rival GfK GFKG.DE. TNS then continued to reject the offer after GfK dropped out, prompting WPP to make its bid hostile.

It has offered 173 pence in cash and 0.1889 of a new WPP share, valuing the group at 260.7 pence per share on Friday, which it described as a 52 percent premium to the share price before the initial GfK merger talks were announced.

TNS has previously urged its investors to reject the offer, saying it undervalued the firm and did not take into consideration how well the business was performing. (Reporting by Kate Holton)