* Outgoing board list claims 12 of 15 seats

* Investor Delfin to take two board seats

* CEO Nagel and Chairman Pagliaro retain roles

MILAN, Oct 28 (Reuters) - Mediobanca Chief Executive Alberto Nagel and his allies withstood opposition from the bank's biggest investor to retain a firm grip on the company in a shareholder vote on Saturday, with the CEO securing a new three-year mandate.

Under Nagel, Mediobanca has moved away from its historic role as a financial holding company and boosted its wealth management and consumer credit operations, also through acquisitions.

But his strategy had come in for criticism, initially from the late Leonardo Del Vecchio, whose holding company Delfin has a 19.7% stake in Mediobanca.

The Italian billionaire, who died last year, had criticised Nagel for being too timid in growing the bank's business and hampering expansion at insurer Generali, in which Mediobanca is the largest shareholder.

Three lists of board candidates were filed ahead of the shareholder meeting in Milan on Saturday, in which shareholders representing 76.8% of bank's capital took part, the highest percentage in 10 years.

A total of 52.6% of voting shareholders, or 40.4% of the bank's capital, backed the slate submitted by Mediobanca's outgoing board, which included a new term for Nagel and won 12 board seats out of 15, Chairman Renato Pagliaro said.

Nagel, at the helm since 2008, had the support of a group of Italian shareholders, representing a combined 10.9% stake in Mediobanca, and of a large number of institutional investors.

Delfin, owned by Del Vecchio's heirs and managed by his former right-hand man Francesco Milleri, claimed two seats for the five nominees it had put forward. It had no seats on the outgoing board.

"We are very happy that Delfin is joining our board and providing a contribution. Critical voices are helpful and positive for us", Nagel said. The Delfin list took 32% of the total capital in the vote.

A small group of institutional investors who had filed a third list took the remaining seat.

While it had stopped short of posing a direct challenge to Nagel, Delfin's decision to put forward its own nominees increased uncertainty in the short term and would have led to a fractured board if its list had been the most voted.

Nagel is expected to be confirmed as CEO at a board meeting on Saturday. Pagliaro will stay on as chairman, a role he has occupied since 2010.

Nagel told shareholders that Mediobanca planned to keep its 13% stake in Generali unless it found a big acquisition opportunity which could be funded with Generali shares. (Reporting by Gianluca Semeraro Editing by Keith Weir)