Marquis drove in a career-high five RBIs, including four on his first grand slam, and Derrek Lee joined the Cubs' 20-homer club in a 9-5 victory over the Mets.
Game 1 of the NL Division Series will be on Oct. 1 at Wrigley Field. Whom they'll play is still to be determined. They could face the Mets, who now lead the Wild Card by one game over the Brewers, who were idle on Monday.
Marquis (11-9) connected in the fourth inning for the sixth slam by a Cubs pitcher and first since Kevin Tapani hit one on July 20, 1998, off Atlanta's Denny Neagle. Marquis also picked up an RBI when he hit into a fielder's choice in the fifth. He's the first Cubs pitcher with five RBIs since Milt Pappas drove in that many on Aug. 11, 1972, also against the Mets.
"He can hit," Mark DeRosa said. "He's got a Silver Slugger. He's a guy who offensively was always putting together great at-bats. We were busting him, because his numbers had been dwindling. He showed it tonight."
"Obviously, I'm just trying to help myself any way possible," Marquis said. "Guys did a good job of getting on base. I just looked for a ball I could hit hard.
"Any time you have a chance to help yourself, why not? I was just looking for a ball I could drive."
This was a special start for Marquis, who grew up on Staten Island and had about 30 family and friends present.
"I can remember, probably, high school, Little League was probably the last [grand slam] I hit," he said. "This was special to do in front of family and friends, and possibly the last time I'll pitch at Shea Stadium."
Marquis actually grew up a Yankees fan, but he went to about three or four Mets games as a kid. He played the New York city championship game at Shea in 1995.
The New York ballparks are so special to him, he was considering going to the last game at Yankee Stadium on Sunday, but the Cubs' charter flight arrived too late. He has good memories of Shea, including pitching in the first game after Sept. 11, 2001.
"That was pretty impressive," manager Lou Piniella said of Marquis' slam. "Plus, he pitched a good ballgame and gave up four runs in about seven innings. The hitting -- they got him out the first time with the same pitch, and the second time up, he really got hold of that ball, a breaking ball that was hanging."
Marquis, who may be the odd man out in the Cubs' four-man postseason rotation, picked up the win, giving up four runs on eight hits over 6 2/3 innings. He was pulled after serving up David Wright's two-run homer in the seventh.
"Every time I take the mound, I feel I'm going to win," Marquis said. "It's always nice to be part of a winning team and feel like you're doing your part to help win."
The Cubs were trailing, 2-1, when Geovany Soto doubled to lead off the fourth. DeRosa singled and Soto scored on Reed Johnson's single, his second RBI hit of the night. Ryan Theriot singled to load the bases, and Marquis cleared them with his second homer of the season and fifth of his career to chase starter Jonathon Niese (1-1).
Two outs later, Lee connected on his 20th home run, off Nelson Figueroa. The Cubs now have five players with at least 20 for the third time in franchise history, in Lee, DeRosa, Soto, Alfonso Soriano and Aramis Ramirez. It's the first time since 2004, when the quintet included Lee, Ramirez, Moises Alou, Sammy Sosa and Corey Patterson. The Cubs also had five players hit at least 20 home runs in 1958, when Lee Walls, Ernie Banks, Walt Moryn, Bobby Thomson and Dale Long did so.
"He responds well when he's rested," Piniella said of Lee, who had Sunday off. "We'll start really resting the team and give everybody an opportunity to play."
A lot of other things went right for the Cubs. Theriot reached base five times. Soto can catch his breath, as Henry Blanco will likely start on Tuesday. And Piniella was able to give such players as Felix Pie and Koyie Hill some at-bats while giving others a little bit of a break.
Getting that home-field edge was huge, as the Cubs finished with a 55-26 record at Wrigley Field.
"It's a step. It's an important step," Piniella said. "You look at all the teams vying for postseason, and the teams that are in have all played well at home. This year, especially, it's important."
"We wanted to make sure we took care of that," DeRosa said. "We're looking at ourselves and saying we put ourselves in this position to give guys rest if they need rest, give guys work if they need work and not worry. There's not so much concern with who we're matched up with -- at least from the players' standpoint. It's nice to win the first ballgame and make sure we have home field throughout."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.