SEATTLE -- In Chris Bassitt’s estimation, he needs more pitch deception. The A’s right-hander was carving his way through the Mariners' lineup on Saturday until he suddenly wasn’t.

Bassitt served up a pair of towering, two-run homers in the fourth inning to lefties Daniel Vogelbach and Kyle Seager, then was charged with two runs after being pulled in the fifth to finish Saturday’s 6-3 loss with a season-high six earned runs.

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“They didn't swing one time at my curveball. Cutter, fastball. That's what I had,” Bassitt said. “So, it wasn't so much about pitch [location]. It was more so just like the speed of pitches, and they were just on that speed.”

Statcast data backs Bassitt’s assertion: he threw just six curves on Saturday, and the Mariners swung at zero. Between his four-seamer and sinker, his fastballs sat at 94 mph and were touching 96, but he was unable to create enough variation in velocity between his cutter, which averaged 87.9 mph. The curve dropped all the way to the high 60s, but Bassitt said that he essentially had to ditch it. Bassitt also threw five changeups, and generated a swinging strikeout of J.P. Crawford with the pitch.

“You're throwing just two pitches, 88 [mph] and 94,” Bassitt said. “That makes hitting a whole heck of a lot easier. Adjustments are going to be made.”

At times this season, particularly over his first month, Bassitt has pitched at an elite level. He had a 2.48 ERA through six starts after returning from a right leg contusion. But he has a 5.89 ERA in his eight starts since, half of which have ended in an A’s defeat, including Saturday.

Vogelbach’s homer came on an up-and-in cutter that he skied to the right-field bleachers at a towering, 43-degree launch angle, and Seager’s -- which snapped an 0-for-21 funk, the longest active streak in MLB -- was on a low-and-in sinker that bled over the plate.

Bassitt denied the notion that he might’ve been tipping his curve, but he admitted that he’ll need to better establish a third pitch, whether it’s his curve or another offering, moving forward. He’s already made a significant adjustment by allocating his fastball usage more to his four-seamer this season, from 13.3 percent usage last season to 26.2 percent, instead of his sinker, down from 43.7 percent to 36.6 percent. And he's picked up more than 1 mph of velocity on his four-seamer, up to 93.7 mph.

And even though the Mariners were spitting on his curve, it’s largely been an effective pitch -- opposing batters are hitting just .151 and slugging .302 against it, per Statcast.

“I felt great. I felt the velo was good. The stuff was good,” Bassitt said. “Again, they were sitting on one speed. If you let MLB hitters sit on one speed for however many games or however many innings or whatever, you're going to get beat. You've got to get them off that speed.”

All the while, Oakland’s offense struggled to manufacture much run support against Mariners lefty Marco Gonzales, who improved to 3-0 in as many starts against the A’s this season.

“He's got good stuff and we've seen him perform really well at times,” A’s manager Bob Melvin said. “He had a little bit of a soft spot there for us and went down. He didn't get off to a great start there, but he's been pitching a lot better. The way he pitched today, he's very capable of doing that.”

Just before his four-run fourth, Bassitt was riding a 2-0 lead thanks to a first-inning sacrifice fly from Ramon Laureano that scored Matt Chapman, and a fourth-inning solo homer by Matt Olson. Laureano added a solo homer in the ninth, but that was all that the A’s manufactured, as they dropped their seventh game to the Mariners in 12 meetings this season.