The Cubs led, 5-1, when Dempster was called upon in the ninth to face the bottom of the order. David Newhan singled to lead off and Ramon Castro flew out to right. The Cubs missed a potential double play as Newhan had to scramble to get back to first. Right fielder Matt Murton couldn't get the throw there in time.
Carlos Gomez then singled, and advanced on indifference. That prompted Cubs manager Lou Piniella to go to the mound for an animated talk with Dempster.
"I said, 'You've got a four-run lead,'" Piniella said of his conversation. "I said, 'Throw the ball.'"
Dempster then walked pinch-hitter Carlos Beltran to load the bases, and said something to home-plate umpire Eric Cooper after ball four. There was an exchange between the two, but Dempster avoided saying the magic words.
He then walked Endy Chavez to force in a run and gave up a single to Ruben Gotay to let the Mets close to 5-3. Dempster was pulled for Scott Eyre, who gave up a first-pitch RBI single to pinch-hitter David Wright, and Delgado followed with his game-winning single.
"I made the pitches I wanted to make," Eyre said. "David Wright, a sinker down and away. I got him to ground out two nights ago on it. This time, he hit it through the infield. I got a ground ball. I'm not going to sit here and whine about it."
Michael Wuertz had pitched 1 1/3 innings, giving up one walk. Will Ohman struck out four over 1 2/3 innings. Then it was Dempster's turn. The bullpen, which now has 11 losses, most in the National League, has been puzzling to Piniella.
"I'll tell you the truth, these guys have to do it," Piniella said of his relievers. "I don't know what else to say.
"We handed the ball over to the closer, and the last time he threw in Philadelphia, I told him it was the best I've seen him throw the ball all year."
The Cubs bullpen is going through a little slump.
"It's the same as hitting -- you struggle and you keep swinging," Eyre said. "You keep playing."
With the loss, the Cubs dropped to 6-13 in games decided by one or two runs, and 2-5 on the East Coast road trip. They're having a tough time getting back to .500.
"I just lost the game," Dempster said. "There ain't much more to say. Throw the ball over the plate and let them hit it, and when I did, they whacked it, and when I didn't, it cost us.
"It's tough when you get ahead of guys and don't put them away, and then fall behind guys and it ends up hurting you," he said. "I put guys in a tough situation of having to come in and save my garbage. It's a tough loss.
"We play a lot more baseball this year and a lot more games, and we just have to bounce back," he said. "They'll ask me to go out and do my job next time, and I have to be ready to go do it. It's tough, it [stinks]. It's happened before, it'll probably happen again. Hopefully, not in the near future."
What contributes to the hurt is that Angel Guzman was in line for his first Major League win. Aramis Ramirez and Angel Pagan each hit a two-run homer, and Ramirez added a RBI single to back Guzman.
The right-hander, who was 0-6 last season in his rookie year, gave up one run on six hits and two walks over five innings against the Mets. Guzman's outing was cut short when he had to leave the game after his at-bat in the sixth inning because of hamstring cramps in his right leg.
"On the mound, I was able to figure out what to do," Guzman said about the cramps, which began when he was pitching. "When I got to home plate, when I tried to swing, I felt like it got real tight, so that's why I said something."
"He was throwing the ball well and competing well, but he had cramps, and we had to get him out of the ballgame," Piniella said.
Guzman, 25, is lucky his teammates were as awake as they were. First pitch on Thursday was 12 hours 17 minutes after the last pitch of their rain-delayed game that began at 10:17 p.m. ET on Wednesday.
Mark DeRosa returned to the Cubs lineup after missing two games with a sprained ligament in his right hand.
"It's one of those things, I'm going to have to hang in there for a couple weeks," DeRosa said. "You ask anyone, I'm sure they have some nick or bruise that's bothering them."
With the game tied at 1 and one out in the sixth, Ryan Theriot reached on an infield single, and Pagan followed with his second home run off a 0-1 pitch that just clear the left-field fence. Alfonso Soriano singled, and Ramirez followed with his 10th home run, another line-drive shot to left. But it wasn't enough.
"There's no words for it," Pagan said. "We're just trying to win a ballgame."
On Tuesday, the Cubs scored 10 runs in a rout. On Wednesday, they managed two hits in an 8-1 loss. They were a little bleary eyed on Thursday from a lack of sleep. They were dazed after this game.
"We just have to get more consistent," Piniella said.