SEATTLE -- If there was any doubt the Astros were in dire need of bolstering their bullpen, Monday’s disastrous loss to the Mariners -- in which Houston blew a seven-run lead -- put the issue front and center only days before the Trade Deadline.

The Astros suffered their worst loss of the season at the start of a rugged eight-game West Coast road trip as the Mariners completed their comeback when Dylan Moore blasted an eighth-inning grand slam off reliever Brooks Raley for an 11-8 win over Houston.

“This hurts a lot,” Astros manager Dusty Baker said. “We made some mistakes with walks to some hitters, the bottom of the order hurt us. A three-run homer. … We couldn't put the horse back in the barn and we didn’t score any more because we know their bullpen is pitching great lately. It doesn’t make you happy.”

It was the first time since May 24, 2000, that the Astros blew a seven-run lead and lost.

With All-Star closer Ryan Pressly not available because he had pitched the previous two games and with the Astros holding an 8-7 lead, Baker turned to Raley with runners at first and second base and two outs in the eighth. Raley walked Tom Murphy to load the bases for Moore, who launched a no-doubt grand slam to send T-Mobile Park into a frenzy.

“[Murphy] did a pretty good job of working back to 3-2 and I needed to execute and I didn’t,” said Raley, who was activated from the injured list Sunday and was pitching for the first time since July 4.

The Astros have been plagued by unreliable relief pitching all season, with the exception of Pressly, who has a 0.47 ERA since the start of June but threw 27 pitches Saturday and 11 more on Sunday. Houston is expected to make at least one trade for a reliever by Friday, but that didn't help them Monday.

Reliever Ryne Stanek started the eighth for Houston and gave up a leadoff single to Ty France before getting two outs. He walked Mariners rookie Jarred Kelenick -- who came into the game hitting .104 -- and Stanek was yanked for Raley.

“The guys they’re sending up there, they were all sub-.200 hitters and we walked the guy that was hitting .100, .102 and at that point we had to make a decision,” Baker said. “Evidently, it wasn’t right and I take full credit for it. … At that point we went with Raley anyway and we took our shot right there.”

After the grand slam, Raley, who had missed up and in with his previous three pitches, hit J.P. Crawford on the fifth pitch of the ensuing at-bat and was ejected from the game, but only after the umpires huddled. Both benches were yelling back and forth and tensions were building.

Baker said crew chief Hunter Wendelstedt told him they didn’t believe Raley’s hit-by-pitch was intentional but they were trying to keep control of the game.

“It was a very calm conversation, and you know Brooks,” Baker said. “He wasn’t trying to hit the guy, but he missed up and in for the third time and hit him with the last one. He certainly wasn’t trying to hit him and [Wendelstedt] didn’t think he was trying to hit him.”

Kyle Tucker, Abraham Toro and Martín Maldonado each homered to help the Astros build a 7-0 lead in the fourth inning. Astros starter Luis Garcia faced the minimum through three scoreless innings before Cal Raleigh got the Mariners back in the game with a three-run double in the fourth. Kyle Seager ended Garcia’s night with a three-run homer in the fifth to cut the Houston lead to 8-6.

“We love three-run homers over here and I’m sure they love them over there, too,” Baker said. “It was just a bad night. They’re going pretty good, but we’ll see tomorrow.”