Locke beat out Kyle McPherson, who was optioned to Triple-A Indianapolis on Wednesday, and Jeanmar Gomez, who will begin the season in the Pirates' bullpen. Gomez is out of minor league options and would have had to clear waivers to be sent down.
"We had extremely challenging decisions," general manager Neal Huntington said. "We didn't have clear separation on a number of fronts, but we still made decisions we feel good about."
Alex Presley, the Pirates' opening-day left fielder and leadoff hitter last season, was optioned to Indianapolis. Presley hit .304 in spring training but has one option remaining. The Pirates kept outfielder Jose Tabata, who struggled last season but who is out of options.
Infielder Jordy Mercer was optioned to Indianapolis and relievers Mike Zagurski, Ryan Reid and Vin Mazzaro were reassigned to the team's minor league camp along with catchers Carlos Paulino and Lucas May, and outfielder Felix Pie.