OAKLAND -- In the three years that Josh Hader has been one of baseball’s best bullpen weapons, the unwritten rule had always been that he does not pitch three straight days. The Brewers made an exception Thursday and paid the price.

Hader took over with a one-run lead in the eighth inning and it was gone in the span of seven pitches, after Robbie Grossman worked a leadoff walk and Matt Chapman followed with a go-ahead home run to straight away center field that sent the A’s to a 5-3 win at the Oakland Coliseum.

• Box score

If the loss hurt, consider the fallout: By pitching Hader all three games in Oakland -- a loss in extra innings Tuesday on Matt Olson’s walk-off home run, a one-inning save Wednesday and a blown save Thursday -- Hader will be limited in another critical weekend series against the Cubs that begins Friday afternoon at Wrigley Field.

“We’ve got a game that we could win, we put him in the game. That’s how it works,” Brewers manager Craig Counsell said. “Any game you lose late, yeah, they hurt.”

Counsell added, “I wanted to use my best pitcher against the best part of their lineup, and we’ll continue to do that. … I would do it again. It just didn’t work today.”

Chapman’s blast spoiled a quality start for Chase Anderson, who limited Oakland to one run on two hits in six innings of a third straight solid Brewers start. Combined with Adrian Houser on Tuesday and Jordan Lyles on Wednesday, Brewers starters allowed three runs on eight hits in 16 innings in the series.

But the Brewers’ other units didn’t do their part, including a lineup that went 1-for-9 with runners in scoring position and stranded 10 men on base. They remain last in the National League at scoring runners from third with fewer than two outs, and tops in the Majors in percentage of runs scored via the home run. 

“We’re capable of doing better offensively, and I think we can and we’re going to have to,” Counsell said. “We’re making it really hard on ourselves.”

Milwaukee took a 3-2 lead into the eighth, where Counsell’s plan was to use Hader for one inning, followed by rising reliever Freddy Peralta in the ninth. Hader went first this time because Oakland’s 2-3-4 hitters were due up.

Grossman’s keen eye came into play as he walked on six pitches to begin the inning. That brought up Chapman. 

“I wanted to hit the first good fastball I could jump on and not fall behind,” said Chapman, who did just that on a first-pitch fastball down and in.

Said Hader, who wanted the pitch down, but away: “That’s his wheelhouse right there, down and in. That’s a pitch he can get the head [of the bat] to. It’s just one of those things where the location wasn’t the best today.”

Whether it was just another misfire or somehow connected to fatigue is impossible to answer. Hader threw eight pitches Tuesday, 10 on Wednesday and 16 on Thursday. What was clear is that it was a different deployment of Hader than previously seen before. Entering this series, he had made only 12 appearances in his career without at least one day of rest.

If the rules of that usage seem confounding sometimes, it is because Hader is so different from everyone else. The Brewers carefully monitor his usage because his all-out style of pitching -- just shy of 90 percent four-seam fastballs -- and his wiry frame mean that he does not bounce back from outing to outing like some late-inning relievers. The Brewers have found that by pitching Hader in multiple innings over fewer games, they can maximize his impact over the course of the season.

The result is that when well-rested, Hader is one of baseball’s best relievers. His 49 percent strikeout percentage is fourth all time for pitchers who have logged 35 innings in a season. Last season, Hader set an all-time record for a left-handed reliever with 143 strikeouts and finished seventh in National League Cy Young Award balloting. Entering Thursday, opponents were hitting .140 against him this season, on pace to be the best mark in baseball history with a minimum of 35 innings pitched.

Most times, the only way to score against him is to hit a home run. Of the 11 games (among 41 appearances) this season in which he has yielded a run, only once did the opponent score without a homer.

Trouble is, Hader is allowing more home runs. Of the 26 hits he’s allowed this season, 11 have been home runs. He has pitched 52 1/3 innings this season, compared to nine home runs allowed in 81 1/3 innings last year.

Now it’s on to Chicago, where Hader will have to settle for being a spectator Friday afternoon.

“We’ve got to focus on the day at hand and not really think about the future,” Hader said. “Obviously, you want to be ready for every game you can, but today’s the day that is important and we’ve got to get the win no matter what’s coming ahead of us. That was one of the tough ones today, so just move on and [play] strong in Chicago.”