OAKLAND, Calif. -- Kansas City Royals manager Ned Yost said it was only a matter of time before the hot-hitting Eric Hosmer hit one out of the ball park.

That time arrived in the top of the ninth inning Friday night when Hosmer launched a solo blast over the center-field wall off Oakland A's left-hander Sean Doolittle, giving Kansas City closer Wade Davis a two-run cushion.

Davis pitched a perfect ninth inning, and the Royals defeated the A's 4-2 at the Coliseum on Friday night, winning their fourth straight game, all on the road.

"I know Doolittle's got a good fastball, so I just wanted to make sure I was on time, ready for it," said Hosmer, who crushed a 1-1 fastball. "Just got a good pitch to hit and finally didn't miss it.

"Been hitting the ball pretty good. Not as much in the air as I'd like, but the last couple days it's really felt a lot better. Any time we're late in the game and we can get some insurance runs with our bullpen, we feel that's huge. It was a big swing for us."

Designated hitter Kendrys Morales had some big swings as well. He went 3-for-4 with his 500th career RBI, keying a 12-hit attack.

Shortstop Alcides Escobar had two hits, walked and scored a run, while Lorenzo Cain went 1-for-3, walked twice and scored once for Kansas City. Shortstop Omar Infante went 2-for-5 with a double and scored a run.

The defending World Series champion Royals, who are off to an 8-2 start, defeated Oakland for the fourth straight time at the Coliseum and for the eighth time in their past nine games overall.

"We realize that coming off of last year a lot of teams are going to be coming for us," Hosmer said. "We're just trying to match the energy levels. I think we've been doing a great job of that."

Royals right-hander Edinson Volquez (2-0) gave up two runs on four hits over six innings for his second win in three starts. He walked four, struck out two and threw 103 pitches.

Kelvin Herrera pitched a scoreless seventh and Joakim Soria a scoreless eighth before Davis notched his fifth save in five chances.

The A's lost their fourth straight game, all at home, and are 1-7 at the Coliseum and 4-7 overall.

A's catcher Stephen Vogt hit his first home run of the season, a solo shot leading off the fourth inning, and went 3-for-4 with two runs. Khris Davis had his first RBI of the season.

A's left-hander Rich Hill (1-2) gave up only three runs on nine hits but lasted just 4 1/3 innings in his third start of the season. He struck out six, walked three and left after throwing 106 pitches.

"They did a good job of hitting the breaking ball and fouled off a lot of good pitches," Hill said. "The two walks in the first came back to bite me. If we have to go to the bullpen in the fifth inning, I'm not doing my job."

A's relievers Fernando Rodriguez, Marc Rzepczynski and Ryan Dull combined to blank the Royals for four innings on two hits before Doolittle gave up a home run to Hosmer.

"He made a good pitch, up and in," Vogt said of Doolittle. "You don't hit the ball to center field on that pitch and you don't hit it out of the park to center at night. Hosmer did an unbelievable piece of hitting."

The Royals jumped to a 2-1 lead in the first inning, using three singles and a walk as Hill threw 30 pitches. Escobar worked a leadoff walk, went to second on Infante's infield single and scored on Cain's single to right as Infante advanced to third. Hosmer hit into a double play, bringing Infante home.

Vogt cut Kansas City's lead to 2-1, launching a leadoff home run into the right-field seats.

The Royals answered with a run in the third, making it 3-1. Cain led off with a walk and moved to second on Hosmer's ground out. Morales singled sharply to center, driving in Cain for his 500th career RBI.

"He had a great night, Yost said of Morales. "It's been a bit of a slow start for him. He's starting to swing the bat like he can."

Vogt hit a leadoff single and scored from second with one out in the fourth when Davis singled sharply to center for his first RBI since coming to the A's in an offseason trade from Milwaukee.

NOTES: A's INF Eric Sogard, who had been on a rehab stint with Class A Stockton for a strained neck, aggravated a left knee injury Wednesday and had an MRI on Thursday. Results are pending. ... Royals 3B Mike Moustakas, who has a sore hamstring, was out of the starting lineup. ... A's RHP Ryan Madson, who pitched last season for the Royals, received his 2015 World Series Championship ring before the game from Yost. "It's always special to give somebody something that they've worked their whole life to get," Yost said. ... A's RHP Sonny Gray changed places with RHP Chris Bassitt in the rotation and will start Saturday against the Royals instead of Sunday. Gray will pitch on his regular four days' rest.