KANSAS CITY, Mo. -- The Kansas City Royals were thrilled not to see J.D. Martinez in the Detroit Tigers' lineup the past three days. But they'll probably see him over the next threewhen they host the Arizona Diamondbacks.

The Tigers dealt Martinez to the Diamondbacks in July, and he is a major reason Arizona has already clinched a National League postseason berth as a wild-card team.

Martinez has hit 16 home runs in September, tying a National League record. He has 29 homers in 59 games with the Diamondbacks and 45 for the year.

Is he surprising even himself?

"If I say yes, it's like I don't think I can do it," Martinez said. "If I say no, it's like I'm arrogant, cocky. It's one of those things where I go up there and expect to hit the ball hard. I just feel like right now I'm having success in being able to do what I want to do up there. I feel comfortable in the box, and I'm getting the results."

While Martinez has tied Ralph Kiner for the NL's September home run record, the major league record is 17, shared by Babe Ruth and Albert Belle.

Martinez is batting .418 with seven doubles and 36 RBIs in September.

Right-hander Zack Greinke, who was a 2002 first-round draft pick of the Royals out of high school in Orlando, Fla., will start the series opener for the Diamondbacks.

This series is a dress rehearsal for the Diamondbacks, who will host the wild-card game Wednesday, a contest Greinke will start. He will be on a limited pitch count against Kansas City.

Greinke (17-6, 3.18 ERA), who is 0-1 with a 3.00 ERA in his career in three starts against Kansas City, is coming off his worstouting of the season. He allowed eight runs on nine hits, including three home runs, and two walks in four innings on Sept. 22 in a no-decision against the Miami Marlins.

The Royals will start right-hander Ian Kennedy, who is winless in a franchise-record 18 consecutive home starts. He is 0-8 with a 6.82 ERA this season at Kauffman Stadium.

Kennedy (4-13, 5.50 ERA) went 21-4 with a 2.88 ERA in 33 starts in 2011 for Arizona. This will be Kennedy's 30th start this season, the eighth straight season he has started at least 30 games.

Kennedy is 2-2 with a 5.93 ERA against Arizona. He has not faced the Diamondbacks since 2014 while with the San Diego Padres.

The Royals will have a slew of free agents after the season, including first baseman Eric Hosmer, third baseman Mike Moustakas, center fielder Lorenzo Cain and shortstop Alcides Escobar, who were all core parts of the 2014-15 clubs that went to the World Series.

This will be their final weekend together, and manager Ned Yost said he plans to play all of them for the fans.

Danny Duffy, who took the loss Thursday, is not looking forward to playing without some of them in 2018.

"It's a hard prospect to think about," Duffy said. "You never think it's going to come to an end. Hopefully, it doesn't. But these guys deserve every right, they've worked their butts off to test the market and they've given everything they have and then some to the city and this organization.

"If they do (sign elsewhere), I'm going to miss them dearly. I think about things. I get sentimental about certain things. It's who I am. It's in my DNA. It's a tough thing to think about. We've played our butts for each other forever."