The loss snapped Boston's four-game winning streak and came after the Red Sox scored 37 runs in a three-game sweep of Texas.
"You can't get caught up on how a team's going -- good or bad," Halladay said after pitching his 39th career complete game. "Sure they were swinging the bats good against Texas. I look at quality pitches. I try to avoid who's hot and who's not."
Indeed, Halladay seemed unaffected by Boston's big numbers in its previous three games. The Red Sox had a 10-run inning and a nine-run frame against the Rangers.
"I don't think he's too worried about who's at the plate," Blue Jays center fielder Vernon Wells said. "He can pause a game plan and work against hitters. He pumps strikes and makes it easier for guys behind him. It's impressive to watch."
Halladay (14-9) improved to 10-4 in his last 16 starts, limiting the Red Sox to six singles before Dustin Pedroia's homer leading off the ninth. He walked one and struck out four in the seven-hitter, holding an opponent to one earned run or less for the 13th time in 32 starts this season.
"He should make a pitching video. He's pretty tough," Pedroia said. "He throws strikes. He's got great stuff and it's tough to get into a rhythm on him because he's creating his own rhythm for himself. We didn't get anything going."
Halladay's outing overshadowed a fairly strong start by Byrd, who was picked up to help the back end of a Boston rotation missing injured knuckleballer Tim Wakefield.
Byrd (7-11), acquired Tuesday from Cleveland for cash or a player to be named, gave up hits to his first three batters -- including Rios' homer. Then he settled down to pitch 7 1/3 solid innings, allowing four runs and 10 hits without any walks or strikeouts.
"I thought it was what we expected," Red Sox manager Terry Francona said. "He threw a lot of strikes, got deep into the game."
After rolling past the Rangers, with the worst pitching staff in the majors, Boston hardly threatened against Halladay and the Blue Jays, who came in leading the AL with a 3.66 ERA.
"Doc is pitching like a Hall of Famer pitches," Toronto manager Cito Gaston said. "He's been doing that for years, when he stays healthy."
Boston's best chance came with two on and two outs in the first when J.D. Drew lined to Wells, who made a sliding catch.
Lind also homered into the Monster seats, making it 3-0 in the sixth. Wells' RBI single made it 4-0 in the eighth.
Friday's series opener was rained out and will be made up as part of a day-night doubleheader on Sept. 13.
Francona said Wakefield, on the 15-day DL since Aug. 12 with tightness behind his shoulder, threw 30 pitches from 60 feet and "felt good." ... Boston had won its last six games at Fenway Park. ... Jacoby Ellsbury, dropped to the bottom of the order for about three weeks when he was struggling, was inserted back into the leadoff spot and went 0-for-4. ... The Red Sox agreed to terms with six draft picks: OF Peter Hissey, OF Ryan Westmoreland, RHP Tyler Wilson, LHP Colby Cervenka, SS Carson Blair and RHP Kyle Stroup. ... Shaun Marcum faces Boston RHP Josh Beckett in the series finale Sunday before the Red Sox go on a nine-game road trip. ... Byrd beat the Blue Jays with a complete game in his previous start last Saturday.