One thing consistent about Royals rookie left-hander Kris Bubic through six Major League starts is he is somewhat of a slow starter but he also finishes strong.

That was the case again Sunday at Guaranteed Rate Field against the White Sox, a 5-2 Kansas City loss in 10 innings. White Sox rookie Luis Robert belted a first-pitch three-run homer off of a slider from Royals rookie Tyler Zuber with one out in the 10th.

It was the Royals’ third walk-off defeat in the past four games.

• Box score

“We’re playing hard,” Royals manager Mike Matheny said, “and it’s fairly clean baseball.”

Added Whit Merrifield, “Obviously we feel like we’re a better team than we were last year. We have guys who have stepped forward. Feel really happy with how our staff has been throwing the ball. We've got to do a better job of finding ways to win, how to win games like this. It’s a learning experience, hopefully.”

Bubic threw probably his best game as a Royal, though getting ahead of hitters continues to be a concern for him.

Bubic got first-pitch strikes to just six of the first 16 hitters he faced, and he was nicked for two runs and five hits through three innings.

But Bubic finished strong, retiring nine of the final 11 hitters he faced, five by strikeouts. Overall, Bubic went 5 1/3 innings and allowed six hits and two runs. He struck out a career-high eight and threw a career-high 106 pitches.

“It was definitely a step up from the last two outings,” Bubic said. “Pitch count was still elevated. I let myself know I could establish command of my fastball inside and out, up and down. And then I was able to add a little, and then attack best I could. I would like to get ahead a little more than I did and have been.”

Matheny agreed, saying, “To see Kris Bubic take his game to another level ... that’s the best we’ve seen him. He was more efficient in the zone, he was using the bottom of the zone. I know there’s another level for him, and he does, too. It’ll be a whole other thing when he can start working first-pitch strikes. But he kept us right in the game.”

Bubic certainly displayed his bulldog mentality in the third. The White Sox already had a run in and had runners on second and third with one out.

With the infield in, Bubic coaxed Robert to pop out to short. Bubic then struck out Danny Mendick on a 2-2 fastball, a foul tip that catcher Cam Gallagher squeezed.

“That was big, keeping our team in the game,” Bubic said. “That is my primary task: to give my team a chance to win. One [run] doesn’t hurt as big as some big, crooked number.”

Meanwhile, the Royals’ offense, which slugged four home runs in a 9-6 win on Saturday, struggled.

Kansas City didn’t get a hit until Gallagher smacked a one-out double into left-center in the sixth. Gallagher then scored on Merrifield's single to left-center.

Gallagher has hit safely in six of his past seven games, and he had four extra-base hits on this road trip.

Merrifield also homered, his seventh of the season, to tie the score at 2 in the eighth.

The Royals had a chance in the 10th with Adalberto Mondesi the automatic runner on second and left-hander Jace Fry on the mound with left-handed hitters Nicky Lopez and Meibrys Viloria coming up.

The Royals opted to have Mondesi try to steal third rather than have Lopez sacrifice bunt him over, which would have set up an unfavorable matchup with Viloria.

“You surrender an out there,” Matheny said, “and then you put all your eggs in one basket with a lefty against Viloria.”

Mondesi was caught stealing, Lopez walked and Viloria struck out. After Merrifield walked, Hunter Dozier struck out.