Rangers general manager Jon Daniels often says it takes about a month for a Major League bullpen to sort itself out for the rest of the season.

Texas doesn't have a month this time around. If the Rangers need that long to fix their bullpen, they are going to plummet out of contention quickly.

“We can’t let this thing go any further,” manager Chris Woodward said after a 6-4 loss to the A's at the Coliseum on Wednesday night. “We have to find guys to step up.”

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The Rangers were hoping Ian Gibaut would do that, but the hard-throwing right-hander gave up a go-ahead, two-run homer to A's catcher Austin Allen in the seventh inning as Oakland rallied back from a 4-2 deficit.

Rangers relievers now have a collective 6.75 ERA during the club’s 3-7 start. Texas has power arms in its bullpen, which has led to 41 strikeouts in 37 1/3 innings. But Rangers relievers have walked 23 and allowed seven home runs.

“We didn’t make pitches to keep the lead,” Woodward said. “It’s tough. We need to win some ballgames, and we need to find a way to win. We need guys to step up and find a way to get things done. ... 3-7 is not the start we are looking for. We need to figure some things out.”

The Rangers have some help coming. Left-hander Joely Rodríguez came off the injured list Tuesday, although Woodward has been reluctant to use him in high-pressure situations right away. Right-hander Rafael Montero is expected to be activated this weekend.

“Hopefully, we can get a little bit solidified,” Woodward said. “I said before, there are no roles. We just need to get outs. We need to be able to maintain a lead. That's really important. And right now, guys just have to find a way to get it done, however they get it done. Keep the ball in the ballpark and get outs, because we desperately need to get it right.”

Rangers starter Kyle Gibson went six innings, allowing three runs on four hits, including home runs to Matt Olson and Ramón Laureano. Gibson had nine strikeouts and two walks, retiring 11 of the last 12 batters he faced.

Gibaut took over in the seventh with the Rangers leading, 4-3, and the A's had the bottom three hitters in the lineup coming up. Gibaut struck out Stephen Piscotty, but he then gave up a single to Tony Kemp on a 1-2 pitch.

Gibaut fell behind, 2-0, to Allen. He threw a 95-mph fastball low and across the plate, which Allen drove out for his first big league home run. Olson's second homer of the night, which came against right-hander Luke Farrell in the eighth, made it 6-4.

"The worst thing you can do right now is put too much pressure on yourself over one game,” Gibson said. “As a bullpen, you can’t feel like you have to be perfect. You can’t feel like you are going out there for Game 7 of the World Series every time. You've got to keep everything in perspective. You have to minimize the pressure and importance of one game.”

Shin-Soo Choo opened the game with a first-pitch home run off Oakland left-hander Sean Manaea, hitting it the opposite way over the left-field wall. Choo also homered on the first pitch of last Friday's game in San Francisco.

It was his 36th leadoff home run of Choo's career, tying Houston’s George Springer and Colorado’s Charlie Blackmon for the most in the Majors since the start of the 2012 season. Choo's 25 with the Rangers ranks second in club history behind Ian Kinsler (29).

Olson hit a two-run home run off Gibson in the first, but the Rangers scored three in the fourth against Manaea. A sacrifice fly by Rob Refsnyder brought home the last of those runs and chased Manaea.

Manaea was followed by relievers Burch Smith, T.J. McFarland and Joakim Soria, who combined to retire 16 of 17 Rangers batters over 5 2/3 scoreless innings.