SAN DIEGO -- While zeros mounted for the Royals’ offense, the walks mounted for starter Brad Keller.

Keller walked a career-high eight batters in 3 2/3 innings Monday night in the Royals’ 4-0 loss to the Padres at Petco Park, while San Diego starter Michael Wacha took a no-hit bid into the eighth inning and struck out 11 Royals in the process.

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Second baseman Michael Massey broke up the no-no with a leadoff single in the eighth inning. Massey and Vinnie Pasquantino -- who snapped a four-game hitless streak with a single in the ninth -- were the only Royals to log a hit in the team’s fourth consecutive loss.

“[Wacha] had the changeup working really well,” Massey said of the pitch the Royals whiffed on 10 times on 25 swings. “It’s kind of floating in there. Just really, really tough as far as the window you’re looking for.

“Every time you wanted to back him up, he threw the heater, and every time you wanted to get him out front, he threw the changeup. He just did a great job of mixing it up.”

Monday was perhaps the lowest point in a bad stretch for Keller, who entered the season looking to be a reliable starter for the Royals. He added a curveball back into his arsenal, introduced a sweeping slider and upped his aggressiveness in spring and early in the season.

In nine starts, Keller has issued a Major League-high 40 walks in 43 1/3 innings while striking out 31. His strikeout-to-walk ratio is 0.78.

“Unacceptable,” Keller said. “Put the team in a bad spot, put the bullpen in a bad spot. Just unacceptable.”

On Monday, Keller threw 94 pitches -- just 39 for strikes. After Fernando Tatis Jr. singled to lead off the bottom of the first inning, Keller got two quick outs but then botched Juan Soto’s slow grounder back to the mound, putting runners on the corners.

Keller sailed a fastball to the backstop to score one run. He walked Xander Bogaerts and threw another wild pitch before escaping the frame without more damage. The Padres’ deep lineup got even deeper when they recognized Keller’s lack of command.

"We were very aware of what the strike zone was early on,” Padres manager Bob Melvin said. “Not trying to do too much, take some pitches, get on base."

In each of the next three innings, Keller issued two-out walks to unnecessarily extend each frame.

“[I] get two quick outs and go out there and walk a guy or two,” Keller said. “Not being able to get deep in the game is really frustrating.”

His velocity was down slightly but nothing physical stuck out to Keller, at least health-wise. The walks conundrum continues to be a delivery issue for the 27-year-old right-hander, who is a free agent at season’s end. In between each of his starts, he’s been working to slow down his arm action and delivery tempo -- speeding up leads to a lack of command.

“I just felt like whenever I tried to correct it, it almost [had] the reverse effect, in a way,” Keller said. “I tried to slow down, I slowed down too much. Tried to speed up, I sped up too much. I couldn’t quite find that happy medium.”

Keller’s sixth consecutive start of four-plus walks leads to questions about his next turn in the rotation. But the Royals lack starting-pitching depth. Kris Bubic is out for the season after Tommy John surgery. Ryan Yarbrough is out for the foreseeable future after being struck by a line drive, and the Royals are still piecing together that rotation spot until Daniel Lynch is able to return from a left rotator cuff strain. Lynch is scheduled to make his fourth rehab start with Triple-A Omaha on Wednesday; the Royals have not announced a starter for that day’s series finale against the Padres.

Kansas City could slot Max Castillo -- who threw 2 1/3 innings on 42 pitches Monday, two days after throwing 80 pitches in the Royals’ bullpen game against the Brewers -- into the rotation. The Royals also could bring back lefty Austin Cox on Saturday, which would be 15 days after he was optioned on May 5.

As far as what’s next for Keller?

“That’s a really good question,” manager Matt Quatraro said. “I’m sure his mind is on a million things, I’m sure the pitching guys are thinking through it. As of right now, I can’t say what would be next.”