A weekend of missed opportunities came to a close in fitting fashion for the Jays (58-70), who were 0-for-9 with runners in scoring position and stranded 10 baserunners to fall a season-high 12 games under .500.
"We haven't been a real good offensive team in a while," manager Cito Gaston said. "We have three guys in the lineup -- [Aaron Hill, Adam Lind and Marco Scutaro] -- that have been hitting all year, and the other guys at the bottom of the lineup have not been hitting all year. It's just been a struggle when you have those guys out there."
Six days removed from an outing in which he allowed more than five earned runs in a non-injury related start for the first time since 2007, Halladay (13-8) surrendered four runs on seven hits and one walk while fanning six, but he could not prevent his third consecutive loss.
"At times, everything was good," said Halladay, who is 2-4 in six starts since the July 31 Trade Deadline that came and went without him changing addresses. "Then you make a bad pitch or two, and teams like this are going to make you pay for it. If you make a couple mistakes here or there, and you don't score runs, it's tough."
Though he had every reason to scoff at the Blue Jays' five-hit effort, Halladay refused to use the lack of offensive backing as a crutch.
"I don't think about it," Halladay said. "My job is to make pitches and not worry about how many runs we're going to score. That's all I try to do. I don't think [run support] changes the way you go out there and pitch. Realizing you're never going to be perfect, you just try to eliminate as many mistakes as you can."
Paul Byrd didn't make many mistakes opposite Halladay, scattering three hits over six shutout innings to pick up a victory in his season debut for Boston.
"He did a good job for them," Gaston said. "That's all I can say."
Two-out doubles by Victor Martinez and Kevin Youkilis put the Red Sox (76-54) on top in the first, a 28-pitch inning for Halladay.
Rocco Baldelli led off the bottom of the second by crushing an 0-1 offering over the Green Monster.
"That wasn't a good pitch," Halladay said. "I tried to throw a cutter down and away and left it up. Sometimes you get away with them and it's a popup, but better teams, they don't miss them. That's why they're a good team -- they take advantage of mistakes and don't miss them very often."
A sacrifice fly from Youkilis stretched Boston's lead to 3-0 in the third, and the Red Sox got to Halladay one last time on Alex Gonzalez's fourth-inning RBI single.
"For the most part, there were times I thought I made good pitches," Halladay said. "But early runs cost you in games like that."
Boston wasn't done, as Shawn Camp's throwing error in the seventh scored two more before Youkilis collected his third RBI of the game with a single to left.
Gaston felt for his ace on an afternoon that oozed with frustration.
"It's a little tough to pitch when you don't get any runs," Gaston said. "They only scored four times off Doc. That's not a lot of runs. We're just not scoring for him, that's all."