Peterson, the Padres' No. 7 prospect, according to MLB.com, was hitting .174 with a .208 on-base percentage and no homers or RBIs in 24 plate appearances over 10 games. At the time of his callup a couple of weeks ago, Peterson had played only 17 games above the Class A level.
"When you get here, winning is what matters, and I didn't help us win," Peterson said.
Still, to be sent back to Triple-A instead of Class A or Double-A is a moral victory for Peterson, who bypassed Triple-A on his way to the big leagues.
"I really learned a lot," Peterson said. "I learned how guys approach the game up here. The guys helped a lot. It was good."
Peterson will play shortstop, third base and second base at El Paso. He has not played second regularly since his freshman year of college, but Padres manager Bud Black wants Peterson to increase his versatility. After all, Peterson mostly played shortstop in the Minors, but he was pressed into duty at third base when Chase Headley was placed on the disabled list with a calf injury.
As for Ambriz, 29, he was 1-0 with a 1.62 ERA in 14 relief appearances for El Paso. He has appeared in 95 Major League games over parts of three seasons with the Indians and Astros, going 3-7 with a 5.37 ERA.
Ambriz made his Padres debut with two innings in relief during Wednesday's 8-0 loss to the Royals. Ambriz allowed two runs (one earned) on two hits with two walks and one strikeout of Billy Butler in the eighth.