PITTSBURGH — Thrust into the third spot in the lineup behind superstar teammate Andrew McCutchen earlier this month, Gregory Polanco knew it might take a while to get settled.

Or maybe not.

The rapidly maturing Pittsburgh Pirates outfielder is so hot at the moment, even his mishits are finding the seats. Polanco crushed a three-run homer off struggling Shelby Miller in the first inning and finished with a career-best five RBIs as the Pirates rolled by the Arizona Diamondbacks 12-1 on Tuesday night.

“You know you’re in the middle of the lineup,” Polanco said. “You’re expected to hit. You’re fighting every pitch, every at-bat.”

Polanco’s shot to the concourse in right-center field off Miller (1-6) three batters in gave Pittsburgh an early boost, even if Polanco flung his bat in disgust figuring he’d just missed it. Instead, it cleared the seats for his sixth home run of the season.

“I thought I didn’t get that one,” Polanco said. “I don’t know but ... (it just) kept going.”

Polanco is hitting .317 (20 of 63) with three home runs and 13 RBIs in 15 games since manager Clint Hurdle elevated him to third in a lineup that is batting an impressive .283.

“You put good hitters at third,” Hurdle said. “It’s been a nice run for him.”

And a miserable one for Miller. His recent recovery from a poor start with the Diamondbacks took a step backward. Less than a year removed from an All-Star appearance with Atlanta, Miller had his ERA rise to 7.09 after surrendering six runs in five innings.

“I feel I’m obviously a better pitcher than this but the results just aren’t there,” Miller said.

“I keep putting the leadoff hitter on base and that keeps hurting me. I’ve got to stop doing it. That’s pretty simple. I didn’t have command of my fastball tonight and it got me into the jams that I wasn’t able to escape.”

Francisco Liriano (4-3) scattered two hits in 5 2/3 innings and added an RBI single as the Pirates improved to 6-2 during a 10-game homestand.

Pittsburgh reliever Arquimedes Caminero was ejected in the eighth after hitting a pair of batters in the head. Caminero drilled 2B Jean Segura in the seventh and Nick Ahmed in the eighth. Segura was sent to the hospital for tests after showing signs of a concussion. Caminero has struggled all season, walking 13 and hitting three in just 17 1/3 innings of work.

“Guys need to keep the ball down and away from the head area,” Arizona manager Chip Hale said. “If a guy can’t do it then he has no business being up here in the major leagues.”