TOKYO (Reuters) - Fuji Soft's top shareholder on Tuesday confirmed its support for KKR's bid for the Japanese software developer at the centre of a $4 billion takeover battle between two of the world's biggest private equity firms.

"As Fuji Soft reaffirmed its support for KKR's tender offer, we believe KKR is the best partner for the company," Singapore-based 3D Investment Partners said in a statement to Reuters.

KKR offered to pay 8,800 yen ($58.67) per share in August, which was followed this month by Bain Capital's 9,450 yen per share bid.

KKR has said it secured commitments from 3D and another large shareholder, Farallon Capital, with stakes of 23.46% and 9.22% respectively, to tender their shares. That would give it control of nearly a third of the company, enough to effectively block a takeover by Bain.

3D said in the statement that it has an irrevocable tender agreement with KKR as part of the process it implemented last year to solicit buyout proposals. While KKR joined the 3D-led process, Bain had declined, saying it was not desired by Fuji Soft.

"KKR has been collaborating with the company on the privatisation for over a year," 3D said, adding that it was confident Fuji Soft would continue to prosper under KKR's ownership.

Bain's counterbid led KKR to switch to a two-stage process that would allow shareholders to take part in an initial tender or a later one, both at 8,800 yen per share.

KKR on Monday extended by 10 working days the first stage of its tender offer, now due to expire on Nov. 5.

($1 = 149.9800 yen)

(Reporting by Makiko Yamazaki and Anton Bridge; Editing by Jamie Freed)