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.¡±