The winning formula for the A’s all year has centered around a dominant bullpen and a sure-handed defense shortening ballgames after taking an early lead.

But on a day where the A’s offense slugged three home runs and took a two-run lead into the sixth, it was a costly error by Marcus Semien and a rare implosion by relievers that sunk Oakland in a 10-5 loss to the Astros in Game 1 of the American League Division Series at Dodger Stadium on Monday afternoon.

Including three Wild Card Game losses, the A’s now have an eight-game losing streak in the first game of a postseason series dating back to the 2006 AL Championship Series, tied with the 1995-98 Indians for the second-longest such skid in history. The 2001-19 Braves (10 straight Game 1 losses) hold the all-time record.

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In the history of best-of-five postseason series, the winner of Game 1 has gone on to take the series 98 of 136 times (72%). That includes 30 of the last 40 best-of-five LDS played since 2010.

The A’s captured their first AL West title since 2013 largely on the shoulders of a relief corps that led all Major League bullpens with a 2.72 ERA in the regular season. J.B. Wendelken took over in the sixth with a 5-3 lead and looked to secure a quick 1-2-3 inning after inducing a grounder against Josh Reddick. But Semien, who was playing on the right side of the infield in the shift, bobbled the ball and then fired his throw to Matt Olson at first in the dirt, allowing Reddick to reach. That error opened a dam for Houston’s offense, as it soon mounted a four-run inning and took a lead that was never relinquished.

Though Semien’s error was costly, A’s relievers faltered against a club they had major success against coming into Game 1 -- Oakland’s bullpen posted a 0.63 ERA over 10 games against the Astros in the regular season. Following the error, Wendelken and left-hander Jake Diekman allowed Houston to score four unearned runs on three singles and a double.

“That’s what the team is all about. We’ve got to try to pick him up,” A’s manager Bob Melvin said of Semien. “Two outs and nobody on, next thing you know they get four runs. You have to give them credit, too. They hit some good pitches to get to that point, even [Michael] Brantley off of Diekman. They were pretty relentless after an opening in that inning and took advantage of it.”

The fact that the error came from Semien does add some peculiarity. After major struggles in his first few seasons with the A’s, the shortstop worked hard to improve his defense to the point where he ended 2019 as a Gold Glove Award finalist at the position.

From Olson’s perspective, the play may not have been as easy as it appeared in real time, as Semien was playing back and had to charge the lightly struck ball.

“It was a tough play,” Olson said. “Reddick is a good runner and hit it off the end of the bat. It was rolling pretty slow and we were in the shift. Marcus had to cut across over towards second base. It happens.

“The things that happened after [the error] just happen like that sometimes. We just have to put it in the rearview and get a win tomorrow.”

The bullpen had to cover some innings after Chris Bassitt was pulled in the fifth. The right-hander was unable to make an early 3-0 lead stick, allowing three runs on nine hits, including a pair of home runs, over just four-plus innings.

Bassitt’s outing was atypical from the recent stretch of success -- the right-hander entered the day with just two runs allowed over his last 33 2/3 innings. Over that period, Bassitt had been able to establish good command by mixing his sinker and cutter up and down in the zone.

On Monday, Bassitt’s pitches caught far too much of the zone. The solo shot he surrendered to Alex Bregman came on a curveball and the two-run shot hit by Carlos Correa came on a cutter, both pitches left over the middle in the fourth inning.

“Everything was up,” Bassitt said. “The ball wasn’t moving the way I was used to it moving. There was no depth to any pitch, and I think you saw that across the board. You throw the ball up, the ball flies here.”

One positive on the pitching side of things for the A’s came in that they got through the loss preserving some high-leverage arms. Melvin stayed away from closer Liam Hendriks, as well as setup man Joakim Soria. Diekman and Yusmeiro Petit, who escaped a tough jam in the fifth, combined to throw just 22 pitches and are also likely available for Game 2.

Another bright spot the A’s can take from the loss is that the offense looked as explosive as ever, jumping on Astros starter Lance McCullers Jr. early with four runs through four innings on a trio of homers by Khris Davis, Sean Murphy and Olson.

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Surprisingly, the offense stalled against a Houston bullpen that had been maligned over the regular season. The A’s were held scoreless over the game’s final four frames.

“They pitched pretty well,” Melvin said of Houston’s relievers. “They have some guys with some velo, too, and matched up a little bit. We just didn’t have the at-bats we typically do at the end of a game. You feel like no matter where you are in the late innings, we have a chance to come back. We just couldn’t do it.”

These A’s have proven to be a resilient bunch all season, most recently bouncing back from a Game 1 loss in their AL Wild Card Series against the White Sox to win the next two contests. They’ll look to that experience as a source of optimism, knowing they’ve been able to handle a situation like this before.

“It’s good to have done it,” Olson said. “Knowing we even have a couple more games in this series is good, too. It happened. We have to look at it like we have to win three out of a four-game series, and we’ve done that plenty of times throughout this season.”