The right-handed Plesac (2-1) allowed a run and four hits, striking out six and walking none. The 25-year-old has a 1.33 ERA in three starts this season.
Plesac hadn't pitched since Aug. 8 after being caught breaking curfew with rotation-mate Mike Clevinger. Plesac and Clevinger were placed on the restricted list and later demoted to the alternate site as punishment. Clevinger returned and made one start last week before being traded to San Diego on Monday, opening a spot for Plesac.
"I definitely had butterflies," Plesac said. "I wanted to come in and give these guys a chance to win.
"This group of guys are special. There has been a lot of learning for myself and my teammates. I think it's something we can look forward and know that we have each other's backs."
Plesac also apologized for a video he posted to social media days after being sent home from the team, in which he complained about his public portrayal and claimed his night out with eight friends wasn't irresponsible. He filmed the video driving a car and not wearing a seatbelt.
"I don't think my words came out as clear as I would have liked them to," Plesac said.
Francisco Lindor and Franmil Reyes homered in the first and Roberto Perez homered in the second, all off Kansas City starter Matt Harvey. Reyes, who had never had a four-hit game, went 5 for 5 with two doubles and a homer.
"I'm seeing the ball well," Reyes said. "I decided to not guess up there. Hopefully I recognize the pitch early."
He did acknowledge that he was thinking about the cycle in his last two at-bats with a homer, single and double.
"Right before the inning started I went to stretch my legs," he said, "just in case."
Harvey (0-2) had failed to get out of the third in his first two starts with the club, but this was his shortest outing yet. He gave up five runs and six hits in 1 1/3 innings, with all the runs coming on home runs.
"They were taking pretty good swings today," was all Kansas City manager Mike Matheny would say about the Indians' offensive attack.
Cleveland's Cesar Hernandez led off the first inning with an infield single, and with one out, Lindor ripped one just inside the foul pole for a two-run home run. One out later, Reyes launched a shot to right center for a 3-0 lead.
Perez extended Harvey's trouble with a two-run home run into the right field bullpen. After allowing another hit and a walk, Harvey was done for the night.
Plesac continued to cruise. He retired 12 straight and faced one over the minimum through four innings.
The Indians added a run in the sixth. Delino DeShields reached on a single and went to second on a wild pitch. Jose Ramirez hit a sharp single off the glove of first baseman Ryan O'Hearn, and DeShields scored.
The Royals finally got a run off Plesac in the sixth when Hunter Dozier lined a home run into the bullpen in right field.
Cleveland got three more runs in the seventh, and one in the eighth on Ramirez's eighth home run.
Royals SS Adalberto Mondesi was not in the starting lineup for the first time this season, but it's for a "mental break," according to manager Mike Matheny. "You give a guy a day off without him feeling like he's been grounded." Mondesi has the lowest OPS in Major League Baseball among players who qualify at .451.
The Indians will send RHP Triston McKenzie (1-0, 2.70 ERA) to the mound in the series finale. McKenzie had a spectacular debut, striking out 10, but struggled a bit in his second start. He gave up two runs on three hits in four innings against St. Louis.
Jakob Junis (0-0, 4.26) will get the start for the Royals. Junis gave up two runs on four hits over 3 2/3 innings in his last start in St. Louis. He struck out six.
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