The Cubs jumped on Keller in the first inning, beating him twice on sliders and once on a changeup as Javier Baez singled, Ben Zobrist doubled and David Bote tripled for a 2-0 lead.
"[Keller] kept us in the game," manager Ned Yost said. "He did a good job of doing that. He made pitches and limited the damage when he needed to. Command was off, the evidence was three walks [later]. But it was off in the first inning, too, on the plate. He was missing quality spots and center-cutting some pitches that they took advantage of.
"I thought he was gonna get out of the first inning scoreless, but kind of threw a slider that Bote hit off the wall in right field for the two runs. But did a good job of regrouping there and giving us an opportunity to win."
Keller, though, then began leaning on his four-seam fastball and tossed three scoreless innings, though he walked three in that span.
"Just two pitches in that first inning -- changeup and a slider were off, and they did some damage," Keller said. "Besides that, I thought the fastball was there and put it where I wanted it."
The Cubs nicked Keller for two more runs in the fifth on four singles sandwiched around a sacrifice fly. Keller gave up seven hits and four runs over six innings. He struck out four.
"That fifth inning snowballed on me," Keller said. "I made good pitches and balls fell in. That's baseball."
Meanwhile, the Royals continued to struggle offensively, this time against former farmhand Mike Montgomery, who threw six-plus scoreless innings. They now have lost 10 straight games when the opponent starts a left-handed pitcher.
YOU GOTTA SEE THIS Royals catcher Salvador Perez continues to nail would-be basestealers with ease lately. Perez threw out his former teammate Zobrist in the third inning, the seventh attempted basestealer Perez has nailed in the last nine tries. Perez has the best percentage in the Majors throwing out attempted basestealers at 50 percent (18 of 36).
"He's a Gold Glover," Yost said. "He's always been a Gold Glover. The thing that impressed me most about Sal the second that I saw him was his release and his athleticism, and his accuracy of his throwing and just how quick he is back there. He just keeps nailing 'em."
HE SAID IT "You definitely notice. I throw a pickoff and got booed at home. Never had that happen before. They travel well." -- Keller, on the overwhelming majority of Cubs fans in attendance
UP NEXT Royals right-hander Heath Fillmyer (0-1, 3.86 ERA) will take the mound in the series finale against the Cubs at 7:15 p.m. CT on Wednesday at Kauffman Stadium. Left-hander Jose Quintana (10-7, 4.12 ERA) will pitch for Chicago. Fillmyer will be making his fifth career start. He took a no-decision in a 6-4 loss to the Twins on Friday, giving up three runs and five hits over three innings before leaving due to a lengthy rain delay.