KANSAS CITY, Mo. -- Eric Hosmer got all of a slider up in the zone, and that pushed the Kansas City Royals up and over the Colorado Rockies.

Hosmer's three-run walk-off homer with two outs in the ninth inning gave Kansas City a 6-4 victory over Colorado on Wednesday night.

Hosmer's blast with Alex Gordon and Melky Cabrera aboard came off former Royals closer Greg Holland (2-5). The first baseman ripped a 1-1 high slider out to right.

"Hopefully this can be the swing for us that we can take into September and into the playoffs," Hosmer said.

It was Hosmer's first career walk-off home run.

"Knocked that off (the bucket list)," Hosmer said with a laugh. "The grand slam, it only took me about seven years, so it's all good. It felt good, though. Especially at a time like this where we're in the middle of the race and we need wins any way we can get them. So that was huge."

Holland has a 21.60 ERA in his past six appearances, taking four losses and blowing three save chances.

"It's all predicated on throwing good pitches at this level, and I didn't do that," Holland said.

Due in part to an ineffective Holland, the Rockies have lost four in a row for the first time since June, and they have dropped 23 of their past 29 road games.

"I think some pitches are up in the zone that are hurting him," Rockies manager Bud Black said of Holland. "The pitch today to Hosmer was up. He's one of the best hitters in the American League. He probably knew Greg a little bit, just how he throws. Just elevated the slider and he got it."

In the ninth, Gordon drew a leadoff walk. After a pair of lineouts, Cabrera singled Gordon to second, setting up Hosmer's winning at-bat.

Brandon Maurer (3-5) worked a scoreless ninth to pick up the victory.

Royals second baseman Whit Merrifield went 4-for-5, matching his career-high in hits. Hosmer added three hits.

"Especially late in the year, this is a big win for us," Merrifield said. "We understood the magnitude at this point of the year what this one meant. To come back like that against an All-Star closer, it's a big win for us."

Charlie Blackmon and DJ LeMahieu combined for six of the Rockies' nine hits.

Neither starting pitcher was scintillating in the early going.

Ian Kennedy gave up a two-out, first-inning home run to Nolan Arenado, the third baseman's 29th of the season. Arenado smacked a 2-0 Kennedy pitch into the Royals' left field bullpen, giving him a major league-leading 108 RBIs.

Gerardo Parra doubled after the home run, but Kennedy struck out Mark Reynolds to end the inning.

In the Rockies' second, center fielder Lorenzo Cain chased down Carlos Gonzalez and Trevor Story fly balls at the wall.

Blackmon led off the Colorado third with his 30th home run, this one landing in the Rockies' bullpen in right.

Colorado right-hander Antonio Senzatela gave up six singles to the first 10 batters he faced. He avoided giving up a run in the first when Lorenzo Cain grounded into a double play.

The Royals scored a run in the second on three singles. Merrifield, who had three hits in his first three-at bats, drove home Mike Moustakas with a two-out infield single.

Story, Blackmon and LeMahieu opened the Rockies' fifth with singles. After Kennedy struck out the dangerous Arenado, Parra's sacrifice fly to left fielder Alex Gordon scored Story.

After Kennedy walked Reynolds, he was replaced by Ryan Buchter. Kennedy, who is winless in 16 straight home starts, left allowing three runs, seven hits and three walks over 4 2/3 innings. He struck out six and threw 95 pitches. He has failed to make it out of the fifth inning in three of his five August starts.

Senzatela gave up two runs on nine hits in five innings.

NOTES: Rockies UT Ian Desmond is scheduled to begin a rehab assignment Thursday with Triple-A Albuquerque. He is on the disabled list with a right calf strain. ... Colorado LHP Tyler Anderson threw a three inning simulated game. He is on the 60-day DL with left inflammation. ... Royals RHP Kelvin Herrera probably will not be placed on the DL after exiting the Tuesday game with tightness in his forearm. It is not anticipated he will miss much time. ... Rockies RHP German Marquez (10-5, 4.24 ERA) and Royals RHP Jake Junis (5-2, 4.99) are the probables for the series finale on Thursday.