Two years of client withdrawals at Pacific Investment Management Co.’s flagship have cost it the title of the world’s biggest bond mutual fund.

Investors pulled $5.6 billion from the Pimco Total Return Fund in April, after redemptions of $7.3 billion in March and $8.6 billion in February, according to estimates from the Newport Beach, California-based firm. With assets of $110.4 billion, the fund fell behind the index-tracking Vanguard Total Bond Market Index Fund, which had $117.3 billion as of April 30, according to preliminary data.

Vanguard’s fund “has definitely benefited from a diverse base of long-term shareholders,” said Katie Henderson, a spokeswoman for Valley Forge, Pennsylvania-based Vanguard Group. “We have advisers, institutions, and individuals who use this really as a core long-term holding.”

Pimco has suffered more than $110 billion of outflows from the fund, which reached a peak of $293 billion in April 2013, since longtime manager Bill Gross left on Sept. 26 for Denver- based Janus Capital Group Inc. The fund, now run by Mark Kiesel, Scott Mather and Mihir Worah, advanced 1.4 percent this year through May 1, outperforming 78 percent of similarly managed funds, according to data compiled by Bloomberg.

Vanguard Total Bond Market Index, a passive fund tracking a broad fixed-income benchmark, returned 0.9 percent in the same period, beating 31 percent of its peers.

Gross, who co-founded Pimco in 1971 and built it into one of the world’s largest investment firms, departed after losing a power struggle with senior executives. He now runs the $1.5 billion Janus Global Unconstrained Bond Fund.

Vanguard also runs an exchange-traded fund version of the Total Bond Market strategy, which holds $27 billion in assets. The firm’s ETFs are run as share classes of mutual funds, a structure Vanguard patented.