The rookie was unhittable to begin the game, except in the most literal sense -- Anthony Rizzo's leadoff single off Fillmyer's foot was the only hit he allowed until the seventh inning. The comebacker, which hit him on the heel, appeared to have little effect, as he at one point retired 12 straight Chicago batters.
"He was just on fire the rest of the game," manager Ned Yost said. "You're right, it got him pretty good. Got him in the heel. But he wasn't limping, or there [wasn't] anything that was noticeable about his delivery. I thought he was still throwing the ball well, so I didn't really worry about it."
The biggest test for Fillmyer came in the seventh, when David Bote and Tommy La Stella singled to set up runners on first and second with one out. After Fillmyer struck out Willson Contreras, Yost came out to chat with him as Tim Hill waited in the 'pen.
Yost said he initially was ready to go with Hill for the dangerous Kyle Schwarber, but when he was about halfway out to the mound, he became unsure. It was when he reached the mound that Fillmyer convinced him otherwise.
"I could see a little glimmer in his eye that he had a chance," Yost said. "I said, 'I don't want to take you out here. This is your first big league win, I want you to win it. I don't want to bring somebody in here to bail you out. I want you to bail yourself out.' He was all fired up with that, so I said, 'Go get him.'"
That proved to be a good decision, as Fillmyer quickly got Schwarber to pop up to Adalberto Mondesi. Getting out of the jam unscathed felt good for Fillmyer, but knowing that Yost believed in him felt better.
"It's always great to get confidence from your manager and to be able to have your manager have confidence in you to stay out there," Fillmyer said.
Fillmyer's success came largely through his curveball that was working possibly as well as it has all season, with additional help from his fastball and slider. To pitch as exceptionally as he did against a powerful lineup like the Cubs' is no easy feat, but Fillmyer thinks his success came fairly simply.
"I didn't have many strikeouts today," Fillmyer said. "I didn't want to walk them. I ended up having two unfortunate ones that didn't end up costing us. That being said, I just let them work ahead and try to get them to get themselves out."
Yost was pleased to see his young starter have success against such a potent offense.
"That's a very formidable team over there, that's for sure," Yost said. "He did a great job of keeping them in check."
MOMENTS THAT MATTERED Butera opens scoring: The Royals offense got Fillmyer some early support in the second when Hunter Dozier led off the inning with a single and Jorge Bonifacio and Brett Phillips each worked one-out walks. With the bases loaded, Drew Butera laid off two pitches before poking a double past third baseman Bote to open a 2-0 lead.
Padding the lead: Mondesi added some insurance for Fillmyer shortly after he was pulled, sending a 74 mph curveball from Jose Quintana into the fountains for a three-run homer. Statcast™ projected his blast as traveling 437 feet at a blistering exit velocity of 106.4 mph.
"That's the excitement that we have with Mondi," Yost said. "He can hit with power from both sides. I mean, big power from both sides. The three-run homer was huge, gave us that breathing room."
SOUND SMART Mondesi's 437-foot homer was the longest by a Royals middle infielder since Statcast™ began measuring.
YOU GOTTA SEE THIS The Royals got two outs in unorthodox fashion in the fifth inning. With Schwarber on first, Ian Happ sent a grounder to Mondesi, who stepped on second for the first out. When Mondesi's throw sailed past first baseman Lucas Duda, Happ took off for second, unaware that the ball bounced back to within just feet of the base. With Mondesi still covering second, Duda threw down to him to beat Happ considerably and end the inning.
HE SAID IT "It felt like a hockey puck off the boot. Coming up I played a lot of hockey, and that's exactly what it felt like. So I knew I had to keep my -- I had to walk it off a little bit. You probably saw me do a couple paces out there. Other than that, it just shook right off and felt pretty good after that." -- Fillmyer on the line drive he took off the heel from Rizzo
UP NEXT Right-hander Burch Smith (1-3, 6.41 ERA) will start the I-70 Series opener as the Cardinals come to Kauffman Stadium for a 7:15 p.m. CT game Friday. Smith has been solid since joining the Royals' starting rotation in July, but allowed six runs in five innings against the Twins on Saturday. The Cardinals will counter with rookie lefty Austin Gomber (1-0, 4.10 ERA).
Jordan Wolf is a reporter for MLB.com based in Kansas City.