The first pillow-whacking was scheduled for 6 p.m., and the fight was still going strong an hour later.
At 6:30 p.m., Guillaume Mirambeau, 28, and Alban Drouet, 25, who hail from France and live in San Francisco, were just getting off of a Muni train at the Embarcadero station, carrying two pillows each and wearing sheepish grins.
They said they tried to go to the Valentine's Day pillow fight last year but it was raining, so this would be their first time. "We're ready," they said.
Meanwhile, Sean Carroll, 22, and Travis James, 23, had just emerged from the fray and were calling it a night.
Dressed in full-body, footed pajamas, or "onesies," they said they had traveled to San Francisco from Folsom for the fight and had held their own.
"It was awesome," said Carroll, who was wearing pink pajamas with bunny-rabbit feet.
Tips for battle?
"Team up and wear a onesie," Carroll said.
Also on his way out was a pillow-less Walter Paulson, 49, best known for singing his comments during the public comment period at San Francisco Board of Supervisors meetings.
Asked where his pillow was, Paulson exclaimed, "It broke all over!"
He said the most difficult part was navigating the flying debris. "The feathers all get in your eyes and everything," he said.
Paulson said he fought hard, and demonstrated his battle technique with an imaginary pillow, swinging his arms to one side then the other, then raising them above his head and whooshing them downward.
"One, two, three," he said, smiling broadly.
A police officer at the scene said at about 6:45 p.m. that there had been no problems he was aware of, and that the crowd was just "having fun."
In past years, cleaning up the plaza and the feather-jammed storm drains has cost the city thousands of dollars. A Department of Public Works spokeswoman said city workers are preparing for another big cleanup this year.