"It was a tough, tough loss," said starting pitcher Rich Hill. "We battled the whole game, and it just came down to a good swing put on that curveball.
"You have to put it away and look forward to the next one."
The Cubs wasted yet another strong performance by Hill, who allowed two runs on six hits over seven innings. Alfonso Soriano, Derrek Lee and Aramis Ramirez each had two hits for the Cubs.
Chicago scored a run after two outs during each of the first two innings against Pittsburgh's Zach Duke. In the first, Lee doubled off the right-field wall and was then driven in by a Ramirez single to left.
Felix Pie singled with two outs in the second and scored when Hill doubled to left. Originally, Pie stopped at third on the play, but he scored when second baseman Freddy Sanchez could not handle the throw from left fielder Bay.
"We started very good," Soriano said. "But we have to finish the game. The first five innings, we played very good, but the last part of the game they [stymied] our offense."
Chicago was held hitless from the third inning until there were two outs in the seventh, when the Cubs loaded the bases after a single by Soriano, a Ryan Theriot walk and a Lee infield single. Pirates manager Jim Tracy called on Jonah Bayliss to relieve Duke, and he induced Ramirez into a flyout to left.
"They left a lefty in to face me, so I should have drove in the run -- simple as that," Lee said about his infield hit. "I've got to have a better at-bat than that. They brought the righty in to face Rammy, a tough righty. When they leave the lefty in in that situation, I have to make them pay right there."
"It was a tough, tough loss. We battled the whole game, and it just came down to a good swing put on that curveball."
-- Rich Hill
That missed opportunity would come back to haunt the Cubs the next half-inning when the Pirates tied the score. A Ronny Paulino double scored Jose Bautista, who got aboard as the only walk of the evening by Hill.
That set the stage for Bay's homer into the elevated seats in right field off Wuertz (0-1), Bay's fourth of the season.
"It's one of those things," said Wuertz, who entered the game with a 0.77 ERA but gave up three long fly balls, the middle of which went for a homer. "[Bay] was aggressive. I was trying to be aggressive, and I just didn't make the pitch.
"It was a hanging slider that got backed up a little bit. With pitches like that, that's what good hitters do. He put a good swing on it. We fought hard. It's just disappointing to lose a game that way.
"He hit it in the right place."
Matt Capps (2-0) earned the win by pitching the eighth, and Salomon Torres picked up his eighth save with a scoreless ninth.
"With the way we played early, it wasn't looking very good," Bay said. "We've been on the back end of a lot of those games that are stolen at the end, and it's nice to be on the front end [tonight]."
The Cubs had the momentum gained from a three-game winning streak before the tragedy of Sunday, when the death of Cardinals pitcher Josh Hancock forced the cancellation of Sunday night's game in St. Louis.
"We were a little flat," Lee said. "It's hard, and you kind of understand it with the events we came off of, with the unexpected day off and the tragedy. We just didn't have the same energy we had the few games before that."
Still, the Cubs didn't come out flat, they just entered a lull midway through the contest. And leaving 10 men on base in a one-run ballgame is as much to blame for the defeat as anything. It was the sixth loss the team suffered when holding a lead in a game, and the defeat dropped the Cubs to 1-9 in games decided by two runs or fewer.
"We had numerous chances," manager Lou Piniella said, "but nothing to show for it."