KANSAS CITY -- The Mariners’ vaunted pitching staff has been on a smooth, steady course for most of the season. But since arriving at Kauffman Stadium for a three-game weekend series against the Royals, that staff has hit a speed bump.

Seattle couldn’t protect a big lead on Friday, and then couldn’t protect a couple of small leads Saturday in an eventual 8-4 loss to the Royals.

This is a Kansas City team that has continually come up with clutch hits over the opening two games of the series, and starter Luis Castillo and reliever Kirby Snead couldn’t escape the Royals' bats, either. Both ran into trouble in the fifth and sixth innings as the Royals scored a combined five runs to take control after Seattle had taken a brief 3-2 lead.

The Mariners, who entered the series having allowed 228 runs -- fifth best in the American League -- have surrendered 18 runs since arriving in Kansas City. When the Mariners won two of three against the Royals in Seattle in May, Kansas City scored eight total runs in the series.

But at Kauffman Stadium, the Royals struck Bryce Miller (seven) and Luis Castillo (five) for season highs in earned runs.

“Their offense has had a lot of success against our pitching, which is new for us,” Mariners manager Scott Servais said. “It has been a struggle here.”

After losing an eight-run lead on Friday, the Mariners were hoping for good things to happen early to signify a fresh start. Sure enough, they got a quick bolt of energy when J.P. Crawford ambushed the first pitch thrown by Alec Marsh for the 11th leadoff homer of his career.

But Marsh settled in and struck out eight through the first four innings.

“He’s got three breaking balls and his fastball is playing up more than usual,” Mariners designated hitter Mitch Garver said of Marsh. “He was locating all his stuff.”

Garver tied the game in the fifth with a homer off the left-field foul pole before a single from Crawford gave Seattle a 3-2 lead. But Castillo couldn’t hold the Royals down.

“For Luis, nothing was easy early in the game,” Servais said. “They were making him work through at-bats. They have bat-to-ball skill up and down their lineup.”

The Royals bounced right back to take the lead for good in the fifth with an RBI single from Nick Loftin and a two-run double from Vinnie Pasquantino.

Castillo allowed five runs on six hits and a walk over five innings, one night after Miller let up seven runs the previous inning.

The Mariners were within 5-4 in the sixth when the recent pitching woes extended to Snead, who allowed a two-run opposite-field double to Kyle Isbel.

“We have not pitched like we normally do the last couple of days,” Servais said. “Ultimately, we couldn’t hold them down. They got a couple of huge two-out, two-run doubles that really spread the gap.”

The Mariners will try to avoid the series sweep Sunday as starter George Kirby looks to cool off the Royals’ hitters.

“They are super aggressive and we haven’t finished,” Servais said. “We got back in the game today, but not enough.”