To make matters worse, a key component of the bullpen, Fernando Rodriguez, is facing a possible disabled list stint with a strained right shoulder suffered Sunday.
"We're trying to get it right," A's manager Bob Melvin said. "We feel like we have a lot of good pieces here. Obviously we've gone through some injuries and continue to go through injuries, which is frustrating. You get to a point where you feel like 'OK, now we've got our guys back we can get on a roll. We played two good series.' And now we have more injuries."
Oakland put a runner on third base with less than two outs in both the sixth and seventh innings Sunday and couldn't score. Stephen Vogt lined into an inning-ending double play in the sixth, while Pirates reliever Neftali Feliz struck out two of the final three A's batters he faced in the seventh after putting runners on the corners to open the inning.
Oakland stranded 22 runners in its three-game series against Pittsburgh, squandered leads in each of the three games, and didn't score a run after the sixth inning in any of the games.
"We found a way obviously to lose games. It's been tough, it's very frustrating," Danny Valencia said.
Valencia, who is hitless in his last 15 at-bats, put most the blame on himself. Josh Reddick came to the plate with runners in scoring position in both the fifth and seventh innings, but failed to convert, saying, "I have to get the job done."
The A's have lost four or more games in a row six times this year. On four of those occasions, the losing streak was preceded by a winning streak. They now sit 12 games below .500 (35-47) after just crossing the midway mark of the season.
Mark Chiarelli is a reporter for MLB.com in the Bay Area. This story was not subject to the approval of Major League Baseball or its clubs.