The moves came after the Dodgers were overwhelmed by Mets starter Jacob deGrom, who struck out 13 in seven scoreless innings.
Mattingly downplayed the lineup changes, saying he hadn't used a set lineup during the regular season, either.
"Yesterday didn't seem that unusual," he said. "Really, our lineups in general, it's a little bit different depending on who is in the lineup that day. Howie really is the only guy out of the ordinary. The only thing I do differently is I make sure he's comfortable. Get him up there, I can put (Justin Turner) up there and get (Andre Ethier) where we want him. "Seems like you make a big deal out of it, but we do this every day. Our guys are actually pretty used to being in different spots. It's not like we're a lineup where every day 1, 2, 3, 4, 5, we know exactly who's playing. We platoon, put people in different spots. I know people make a big deal out of it, but it's really the ordinary for us."
Kendrick has not started in the leadoff position all season, but he had a double and single in four at-bats in Game 1.
The 21-year-old Seager, the youngest Dodgers position player to start a postseason game (previously 22-year-old James Loney), went 1-for-4 in the No. 3 slot with two strikeouts, the only hit being a misplayed double. Pederson, who slumped throughout the second half, went 0-for-3 with an intentional walk.
"I thought he was fine," Mattingly said of Pederson. "We didn't do a lot with deGrom. I thought the matchup is better with Kike."
On Seager, Mattingly said: "I thought he was fine, as good as anybody else. The first at-bat looked a little bit quick. After that I thought he was fine."
Mattingly said Grandal's rapport with Greinke was a factor in his starting over A.J. Ellis.
Howie Kendrick, 2b
Corey Seager, ss
Adrian Gonzalez, 1b
Justin Turner, 3b
Andre Ethier, rf
Carl Crawford, lf
Yasmani Grandal, c
Enrique Hernandez, cf
Zack Greinke, p
Aside for some minor shuffling, the Mets made just one significant lineup change from National League Division Series Game 1 to Game 2, subbing rookie Michael Conforto into left field over Michael Cuddyer. The move was planned against Dodgers starter Zack Greinke; Conforto started regularly against right-handed pitchers after his late-July call-up, posting an .872 OPS against them.
Conforto was 0-for-2 with a hit-by-pitch in his first meeting with Greinke on July 26, two days after his call-up.
"Well, as I just talked to our beat guys, the only thing that changes the game here is that it says postseason in front of it," manager Terry Collins said. "It's still play. They've still got to throw strikes, and [Conforto] can swing the bat. He can hit. He can stinking hit. And I don't think the fact that you're playing in Dodger Stadium, even though it's the postseason, is any different. You're still facing Zack Greinke. That's a challenge for anybody.
"But this guy can swing the bat, and I have all the confidence that he's going to walk up there with that short stroke and hopefully get something he can put the bat on. I mean, look at the Dodgers, they've got a rookie hitting third. So if you can hit, you can hit."
The Mets also flipped Daniel Murphy from fourth to third in the lineup Saturday, moving Yoenis Cespedes into the cleanup spot. They did likewise with Lucas Duda and Travis d'Arnaud in the fifth and sixth holes.
There was some thought that Collins might start Wilmer Flores over Ruben Tejada at shortstop for Game 2, given Flores' success (3-for-8) off Greinke in a small sample size. But the Mets instead stuck with Tejada, who drew a key walk during the Mets seventh-inning rally in Game 1.
Curtis Granderson rf
David Wright, 3b
Daniel Murphy, 2b
Yoenis Cespedes, cf
Lucas Duda, 1b
Travis d'Arnaud c
Michael Conforto, lf
Ruben Tejada, ss
Noah Syndergaard, p