The left-hander escaped jams in each of the first four innings, blanked Toronto through six and helped the Boston Red Sox to a 5-1 win Thursday night and a three-game sweep of baseball's highest-scoring team.
The Blue Jays were held to five runs in the three-game series, only one off Lester (3-4).
"As he got into the flow of the game, he got better," manager Terry Francona said. "As he feels good about himself, he'll relax a little bit."
Lester was 16-6 last season and emerged as the co-ace of the staff with Josh Beckett. But he had allowed 13 earned runs in 10 innings in losing his two starts before Thursday. He held Toronto to one run on eight hits in 6 1-3 innings with four strikeouts and one walk.
"You hit a little bit of a rough patch, you think you can't get anybody out," Lester said, "so you need to just get back to the basics of throwing strikes and throwing to halves of the plate" instead of aiming for the corners.
The sweep cut Toronto's AL East lead to a half-game over Boston, 15-2 in its last 17 home games.
"I don't think anybody in this clubhouse is happy," Blue Jays manager Cito Gaston said before leaving for a three-game series in Atlanta. "We certainly have to put this behind us and move on and go down to Atlanta and see if we can play a little better baseball."
Lester got the support he needed in a three-run first. Two came on Jason Bay's 11th straight homer with runners on base, a club record. His opposite field shot into Boston's bullpen in right field was his 13th of the season, second most in the AL.
"To hit it that far, he's got some strong wrists on him," Francona said.
Boston led 5-0 before Aaron Hill singled in Toronto's run in the seventh.
Toronto fell to 4-5 against AL East opponents -- 3-0 against last-place Baltimore and 1-5 against Boston and the New York Yankees.
"If we are going to be in first place, we will have to beat the Sox and the Yanks," Lyle Overbay said. "We can beat these teams. We just have to figure out how."
Bay broke a tie with Kevin Youkilis and Tony Conigliaro for most consecutive homers by a Red Sox player without a solo shot. He is one behind the major-league record set by Hank Aaron in 1970 and tied by Ken Griffey Jr. in 1999.
Lester left with one out in the seventh after a walk and a single put runners at first and second. Hill then lined an RBI-single to left off Ramon Ramirez before Adam Lind ended a bases-loaded by fouling out to Bay in left field.
Youkilis then walked and scored on Bay's homer that hit the top of the five-foot high fence in front of Boston's bullpen, just beyond the reach of Alex Rios.
The Red Sox made it 4-0 in the third on Pedroia's double and Youkilis' RBI single. They scored their last run in the fifth on Pedroia's RBI single.
Ortiz went 1-for-4 one day after breaking a career-long 149 at-bat homerless drought. ... Toronto lost to Boston for the 10th time in 13 games. ... John Smoltz allowed one hit and struck out two in three innings of his first rehab stint. He pitched for the Red Sox Single-A team in Greenville, S.C. at the Augusta, Ga., affiliate of the San Francisco Giants. ... Daisuke Matsuzaka makes his third start of the season Friday night and his first since going on the disabled list April 15 when he faces Johan Santana and the New York Mets.