* Bain gets 87 pct of Asatsu-DK
* U.S. PE firm had sought minimum more than half
* Top shareholder WPP dropped opposition (Adds ADK comments, background)
TOKYO, Dec 7 (Reuters) - U.S. private equity firm Bain Capital has won enough shareholder support to complete its tender offer of Asatsu-DK Inc (ADK), allowing the Japanese advertising agency to end a bitter two-decade partnership with top shareholder WPP.
Bain received 87 percent in the tender offer of Japan's third-biggest ad agency, at 3,660 yen ($32.55) each, a regulatory filing showed on Thursday. It had been seeking more than half of ADK to take it private in a 152 billion yen ($1.35 billion) deal announced in October.
Britain's WPP, the world's biggest advertising group and ADK's largest shareholder with a 25 percent stake, had initially tried to block Bain's tender offer, which it said undervalued the company. But it reversed its position last month after agreeing to discuss plans to reinvest in ADK at a later date. Bain's final offer price was unchanged from the original.
The deal effectively ends the alliance between WPP and ADK, forged in 1998 to jointly cultivate clients and set up ventures. The partners never got along, and towards the end of their affair they bickered over digital strategy and what to do with loss-making overseas operations.
"Today's successful tender offer close is an important milestone in ADK's growth story and we are confident that Bain Capital is the right partner to take us through this next phase of transformation," ADK CEO Shinichi Ueno said in a statement.
Bain's acquisition will allow ADK to focus more on fast-growing areas such as mobile video advertising, while WPP may be able to maintain access to the world's third-largest ad market - worth about 6.2 trillion yen ($55 billion) - through a stake in the Bain-led investment vehicle.
The Japanese agency said last month WPP and Bain would discuss the possibility of WPP holding about 25 percent of an entity that would own ADK.
Like other advertising markets, Japan is undergoing a rapid transformation as money moves from traditional media outlets to digital. The industry is largely controlled by Dentsu and Hakuhodo DY Holdings, with ADK a distant third.
The deal marks Bain's second major acquisition in Japan this year after a consortium it led agreed to buy Toshiba Corp's memory chip business for $18 billion.
Expectations that Bain would raise its offer price drove ADK's stock to as high as 3,980 yen, a year-high, versus 3,170 yen on the day the bid was made. ADK shares ended morning trade at 3,660 yen on Thursday. ($1 = 112.3700 yen) (Reporting by Junko Fujita; Editing by Chang-Ran Kim and Stephen Coates)