Coupled with the addition of Coco Crisp, who made his Oakland debut on Friday, Ellis' return has given A's manager Bob Geren the lineup he expected to see this season.
"It's kind of the team in Spring Traning you envisioned," Geren said. "Looks like almost everyone is back in there at this point, and it's a good feeling to have.
Crisp remained as Oakland's starting center fielder, hitting leadoff, while Ellis occupied the No. 6 slot Saturday.
Rosales spelled Kevin Kouzmanoff, who has played in every game but one this season, as the A's starting third baseman.
Geren said Rosales will likely be filling in for shortstop Cliff Pennington and first baseman Daric Barton on occasion throughout the season.
"That's what we really need to stay healthy -- is have flexibility and the utility of a guy like Rosales," Geren said.
Geren also said Jack Cust will become the team's primary designated hitter now that Eric Chavez has been placed on the 15-day disabled list.