They have baseball's worst record against left-handed starting pitchers, a significant statistic even for the Cubs.
"It's almost a fluke," manager Dale Sveum said. "Coming into the season, I thought that one of our strong points would be when left-handed pitchers faced our team.
"That's because we could stick a lot of right-handed hitters out there who had really nice careers against left-handed pitching. It's not that they're doing horrible; we're just not getting the slugging percentage at all against left-handed pitching, which is holding us back from scoring multiple runs in an inning."
Against Red Sox starter Franklin Morales, who had made 145 straight relief appearances, the Cubs did their usual. They struck out nine times in Morales' five innings and trailed 3-2.
"You can't even try to do what we do against left-handed pitching," Sveum said. "It's very difficult to have those kinds of numbers on a consistent basis."
Cubs lefty Paul Maholm started and gave up two runs in the first and a David Ortiz homer in the fourth. The biggest damage came after he left. The Red Sox scored three in the seventh with the help of a Cubs error and a questionable cutoff play.
Maholm's record remains 4-5, showing that other teams aren't having as much trouble against lefties as the Cubs.
Of course, the Cubs are having trouble scoring against right-handers too. That was a problem in the past as well, so new general manager Jed Hoyer added David DeJesus in right field, Ian Stewart at third base and gave the first-base job to Bryan LaHair.
Those three are left-handed hitters, but they have sat against left-handed pitchers, especially lately, and all are hitting below .200 against southpaws.
Sveum said he has thought about defying the book and playing them against all pitchers, but they "just are not doing anything on a consistent basis against left-handers to warrant that."
That is not good news to LaHair, who is trying to prove to the Cubs — and other teams that might have interest in trading for him — that he can hit any pitcher.
"There's no question I want to play every day," he said. "But this is a team thing, and right now (Sveum's) got a right-handed lineup. He wants to get guys at-bats. This seems to be the year of opportunity with the Cubs, and guys deserve an opportunity like I got.
"I feel like my time will come. It's not something I really want to fight and battle right now. I know I'm an everyday player, and I still believe I'll be in there against lefties."