"I've seen some bombs," teammate Cliff Floyd said, "but that was one of the longest ones I've seen."
Ramirez hit a drive deep into the second deck of stands down the left-field line to make it 7-1 in the sixth, Chicago's first grand slam since Derrek Lee connected on Sept. 6 against Pittsburgh. The Cubs had been 0-for-17 with the bases loaded dating to April 30.
"It doesn't matter how far it goes," Ramirez said. "It's a home run."
Floyd had three hits and an RBI in his first game at Shea Stadium since spending the previous four seasons with the Mets, and Chicago handed John Maine his first loss of the year.
Playing first base because Lee is out with neck spasms, Daryle Ward hit a two-run double in the first. Michael Barrett doubled twice and drove in two runs, and left fielder Alfonso Soriano threw out a runner at the plate in the second to keep the score 3-0.
"We played well," Cubs manager Lou Piniella said. "Let's hope we can do this with some consistency."
Zambrano started a six-run rally with a one-out single in the sixth. With two outs, Ramirez connected off Scott Schoeneweis for his seventh career slam.
Barrett added a run-scoring double and Jacque Jones had an RBI single in Chicago's largest victory of the season. The Cubs finished with 15 hits.
"We've got to just play and know how good we are and know what we're capable of doing," Floyd said. "This team is set up to go out and bash guys in."
Zambrano (4-3) allowed six hits, walked three and struck out three. He threw 116 pitches and has won three of his past four starts.
"Hopefully, this can be the start of a streak," Zambrano said. "That was the best I've felt."
Shawn Green hit his fifth home run for the Mets, who had won five of six and nine of 12. Carlos Delgado left in the seventh, one inning after he was hit on the left hand by Zambrano's pitch. X-rays were negative and he is day to day with a bruised pinky.
"I'm good. I got hit where I got hit the other day, about three weeks ago, so it swelled up a little bit," Delgado said. "I'll put ice on it a couple of times tonight. We'll see tomorrow."
Maine (5-1) was tagged for seven hits and three walks in five innings, though he gave up only three runs. The NL pitcher of the month for April, Maine saw his ERA rise from 1.79 to 2.15. The Mets fell to 7-1 in his starts.
"They were waiting on my fastball, they were waiting on it. My curve got better. You've got to adjust a little bit," Maine said. "When I started getting my curve over later in the game, it made my fastball better. I've got to stop walking people in the first inning."
Indeed, Floyd said he was asked about Maine, his former teammate, in the Cubs' meeting and told his new club that the right-hander liked to rely on an effective heater. Chicago sure looked ready for it.
After consecutive walks in the eighth that pushed Zambrano's pitch count to 113, Piniella visited the mound but left the right-hander in the game.
"This was as good an outing as he's had all year," Piniella said. "He wanted to stay out there. He wasn't going to throw 115 pitches."
Piniella let Zambrano bat in the ninth, then pulled him. Scott Eyre finished up on the mound.
"Zambrano was much, much better. He worked with our pitching coach on staying on top," Piniella said. "He pitched really well. We were looking forward to this. A nice game for him, a nice game for our team."
- Cubs INF Mike Fontenot, called up from Triple-A Iowa before the game, entered as a pinch hitter in the eighth and doubled off Ambiorix Burgos for his first major league hit.
- Piniella said INF Mark DeRosa, who strained a ligament in his right hand on a play at first base Monday night, probably won't be able to play for a few days except in an emergency.
- Floyd played RF and batted second. He got a nice ovation before his first at-bat. "It felt great. You never know what it's going to be," he said, adding it was "definitely weird" to see ex-teammates such as David Wright and Jose Reyes on the other side.
- The Mets acquired minor league INF Jake Gautreau from Cleveland for a player to be named or cash. Gautreau was picked 14th overall in the 2001 draft out of Tulane.