After months of deriding U.S. Treasury bonds, Bill Gross and his fund managers at Pacific Investment Management Co. have switched sides.

Pimco had been the biggest and most vocal of a large group of Treasury bears, predicting that Treasury prices would fall, and yields rise, as the U.S. economy strengthens and the government borrowing binge continued.

In the opposing camp was Pimco’s chief rival, BlackRock Inc., which said in March that it was buying up Treasurys.

So far, BlackRock’s view has proven to be the winning bet. The debt crisis in Europe sparked a global flight to safe-haven assets.

Pimco on Wednesday shifted its views on Treasurys to be more in line with BlackRock’s. The capitulation by Mr. Gross and Pimco, which has some $1 trillion in assets under management, is significant because it is among the most influential players in the market. Pimco has enough money to move the market and investors follow its opinions closely. Mr. Gross and his Pimco colleagues regularly appear on television and release monthly newsletters espousing their views.