PHOENIX -- The D-backs dubbed this weekend a “Marte Party,” with a number of promotions including a Ketel Marte bobblehead night on Saturday designed to encourage fans to vote for Marte in Phase 2 of All-Star Game voting, which kicks off on Sunday.

For a while, Friday night’s game against the A's cooperated. Marte doubled to lead off the game and gave the D-backs a late lead with an RBI single in the seventh. Things could not have looked better for the home team.

Ryan Thompson, who got the last out of the seventh, was set to pitch the eighth with closer Paul Sewald ready to get the ninth.

"I felt like, game over,” D-backs manager Torey Lovullo said. “Thompson to Sewald. Book it."

Instead, the A’s scored three runs off Thompson in the eighth and another three in the ninth off Brandon Hughes for a 9-4 win that left the D-backs stunned.

"It just didn’t happen,” Lovullo said.

Since the D-backs signed him last August following his release by the Rays, Thompson has been one of the team’s best relievers. He, Sewald and Kevin Ginkel formed a shutdown trio last year and were a big reason why the D-backs were able to capture the final NL Wild Card spot and go all the way to the World Series.

Coming into Friday, Thompson had allowed just four runs all year and sported a 1.13 ERA. Thompson had not allowed more than one run in each of his 43 appearances before Friday, spanning 45 innings.

So it was truly stunning to watch Tyler Soderstrom lead off the eighth with a game-tying homer against him. One out later, Thompson issued a walk and then allowed an RBI triple to Zack Gelof and a run-scoring single to Max Schuemann.

The D-backs suddenly trailed 6-4 and Thompson was left searching for answers.

"Just wasn't my best tonight and I wasn't making adjustments when I needed to,” Thompson said. "Simple as that."

"What did I see?" Lovullo asked. "A lot of two-seam fastballs that laid over one another. He didn’t change [the hitter’s] sightlines, he didn’t mix in the slider. He’s got a really good slider."

In Thompson’s mind, it wasn’t the type of pitches that he threw that did him in -- rather, it was the mechanical issues that he couldn't fix in the middle of the inning.

"We're expected to do the same delivery thousands of times in a season,” Thompson said. "To do that is near impossible. So when you throw some where it’s not perfect, how do you make that adjustment to get to what you’re looking for? It wasn’t a strategy thing tonight. It was that I wasn’t good tonight and I didn’t make the right adjustments. I made adjustments, they were just bad adjustments. And that'll happen. That's what you learn from. You learn ‘OK, when I'm feeling this, don't do that.'"

With his mechanics off, Thompson was throwing pitches that were good but not for strikes. And when he was making bad pitches, those were strikes. Very hittable strikes.

That’s not a formula for success -- it’s a recipe for disaster.

When Thompson has mechanical issues, he’s usually able to make the correction on the mound. Friday, it didn’t happen until he got back in the clubhouse.

"It's frustrating to fix it after I get off the field, but it's better than not fixing it at all,” Thompson said.

The D-backs have some fixing of their own to do. After beating the Phillies in their series opener against them last Friday and reaching the .500 mark for the first time since April 16, Arizona has dropped five of six.

The NL Wild Card race is still wide open at the moment, but with the Padres, Cardinals and Mets heating up, Arizona can’t afford to fall too far behind. The club certainly can’t afford to lose games with late leads to teams like the rebuilding A’s, who came into the game with the second-worst record in baseball.

"You can't make an assumption that just because it’s the Oakland A’s, you’re going to walk through them and beat them three games,” Lovullo said. "That's a well-run team. They've got a good manager [Mark Kotsay] there."