The Pimco Income Fund, widely seen by investors and analysts as Pimco's new flagship fund, posted $1.6 billion of inflows, resulting in assets under management of $73 billion, Morningstar said.

Pimco Income, which is overseen by Group Chief Investment Officer Dan Ivascyn, has been popular as an income-oriented alternative in the continuing low-yielding environment, while Pimco Total Return, once the world's largest bond fund at a peak of $292.9 billion in assets, has had mixed results.

Todd Rosenbluth, director of ETF and mutual fund research at CFRA, said total returns for Pimco Total Return are in the bottom quartile of its Lipper peer group on one-year and three-year bases, while Pimco Income is in the second quartile in the past year and the top quartile on a three-year basis.

"Investors should dig deeper to understand the differences between them – including the lower interest-rate sensitivity of the Income Fund – but for many, the stronger relative performance matters a lot," he said.

"While money continues to shift to passive strategies, active fixed-income funds that perform well will continue to gather assets."

For its part, Morningstar ranks the Pimco Total Return Fund in the second quartile on a one-year and three-year total return basis.

The Pimco Total Return Fund, which has posted returns of 2.61 percent for the one-year period ended Feb. 3, is surpassing 55 percent of its category peers on a 12-month basis and exceeding 52 percent of its category peers on a three-year basis.

The Pimco Income Fund ranks in the top quartile on a three-year period, returning 8.48 percent on an annualized basis, Morningstar said.

Pimco's Ivascyn said Pimco Total Return has had a strong start to the year, returning 51 basis points over its benchmark in January. "Given the political and policy uncertainties in 2017, we expect there to be more opportunities in the market for investors who actively pursue them," Ivascyn said.

(Editing by Paul Simao and Matthew Lewis)

By Jennifer Ablan