PHOENIX -- Entering Monday night, the only MLB team to walk less than the Royals were the D-backs, a contact-oriented and free-swinging lineup with a Major League-worst 5.3% walk rate.

But against the Royals, the D-backs won because of the walks they took.

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In the eighth inning, Royals reliever Aroldis Chapman issued just his third walk this year and saw it come around to score for the first run he has allowed in 2023 -- which just so happened to be the winning run in the Royals’ 5-4 series-opening loss to the D-backs at Chase Field.

The Royals issued eight walks Monday, including starter Brad Keller’s career-high six on a night when he didn’t have command of his breaking balls and the D-backs weren’t offering at any below the zone.

After starting the season with a 2.12 ERA through his first three starts -- and 16 strikeouts in 17 innings -- Keller has walked 11 in his past two starts.

“Especially for a team that was really aggressive, they weren’t swinging at anything,” said Keller, who allowed four runs in four innings. “Early on, I threw some good sliders right below the zone, and they didn’t offer anything. That was frustrating. … I’ve just been digging myself a bunch of holes with these walks. It’s frustrating.”

This season, Chapman has looked like the dominant closer he has been in the past, which is what the Royals had hoped for when they signed him to a one-year deal this offseason. In eight innings before Monday, he struck out 15 without a run scored.

With one out, the Royals took exception to a pitch timer violation that home-plate umpire D.J. Reyburn called on Chapman. Chapman was coming set before pinch-hitter Christian Walker was engaged toward the mound. The second time Chapman did this, Reyburn called for an automatic ball.

“I did not agree with that,” manager Matt Quatraro said. “… There’s a lot of subjectivity to that.”

The result of the plate appearance? A walk.

“I got up and told Chappy in Spanish, because maybe he didn’t understand the umpire,” catcher Salvador Perez said. “So the second time, I get up and tell him in Spanish, ‘Hey, wait until you see the guy look at you,’ and [the umpire] called a ball. I don’t know exactly what the rule is. It’s kind of confusing.

“And that’s no excuse. But maybe it [turns out] different. Because he walked that guy.”

Walker went to third on Gabriel Moreno’s single and scored on Nick Ahmed’s pinch-hit cue-ball grounder to first baseman Vinnie Pasquantino. The ball came off Ahmed’s bat at 30.4 mph and  took an odd spin, which made it hard for Pasquantino to grip it as he threw home. Instead of landing in Perez’s glove, the ball hit Walker as he slid across the plate for the winning run.

“That ball was -- you can’t play for that,” Quatraro said. “I thought Vinnie made a nice attempt. It was a squibbler, it’s hard to get a grip on it. It was going to be a bang-bang play at the plate. But how do we like our chances? Any time Chapman comes in the game, we’re anticipating a zero.”

The Royals needed a zero after tying the game in the top of the inning with an offense that has shown signs of life recently. With Michael Massey on first base, Nicky Lopez drew a pinch-hit walk against lefty closer Andrew Chafin, followed by Kyle Isbel's game-tying single.

“Chafin’s a really good reliever,” Quatraro said. “And for Nicky to go up there and work the walk, Izzy to get the base hit left-on-left, those are both really good signs. Massey was on base there as well in the inning. There were a ton of positives, just a frustrating way for it to end.”

In the end, the Royals were aggressive instead of patient like the D-backs. Perez and Franmil Reyes struck out swinging to end the game and chalk up another heartbreaking loss in a season full of them so far.

“It was an exciting game until the last inning,” said Perez, who was 2-for-4 with two RBIs. “I should have gotten a walk on that pitch [a slider in the dirt]. I was too aggressive and tried to do some damage when they didn’t even throw a strike to me. I’ve got to be more patient.”