The lefty is 5-7 with a 4.80 ERA in 19 starts this season and is winless in his past three outings. His previous start was one of his worst of the season, lasting just four innings and surrendering six runs on seven hits against the White Sox.
"It just keeps adding on, and I'm getting tired of it," Lester said. "I try to make adjustments, try to do the things I need to do and I'm just not getting results. I've got to do a better job of executing pitches, I'm just not doing it right now.
"I feel fine mechanically, feel fine with the process. When the ball is leaving my hand, I'm not in the part of the zone that I need to be, I'm up a little bit and I don't know what it is. I just got to keep throwing the ball, it'll turn."
Sunday's finale against the Blue Jays at Fenway Park could help Lester turn that corner. Since 2011, Lester is 4-1 with a 2.78 ERA in seven starts against Toronto. For his career, he has held the Blue Jays to a .195 batting average, which is the second-lowest average against him among American League teams.
While the Blue Jays will have their hands full with Lester, Toronto will start righty Henderson Alvarez in the finale as it aims to complete a three-game sweep of Boston.
Against the Red Sox, Alvarez is 1-1 with a 3.09 ERA in four career outings, including a win on June 25 at Fenway, when he pitched five innings and gave up three earned runs before exiting with right elbow soreness in the sixth.
The elbow soreness didn't cause the righty to miss any starts, but he is winless in two July outings. Alvarez struck out a career-high-tying six batters during his last outing -- six innings of two-run ball against the Yankees. He labored early, but he turned in his 10th quality start of the season despite not factoring in the decision.
"I felt like the first couple innings, I was dropping my elbow down and the ball was just taking off and [stayed] up in the zone," Alvarez said after his last start. "I made the adjustment on that, got on top of the ball and got more strikes."
Blue Jays: Forearm tightness lands Frasor on DL
Toronto placed right-handed reliever Jason Frasor on the 15-day disabled list Saturday with tightness in his right forearm. Frasor has dealt with soreness throughout the season, but the discomfort reached a new level while warming up Friday.
Frasor is 1-1 with a 4.00 ERA and 45 strikeouts in 36 innings of relief. He ranks first on the Blue Jays in appearances (42) and holds (12) this season.
Red Sox: Saltalamacchia homers in return to lineup
Catcher Jarrod Saltalamacchia returned to Boston's lineup in a big way Saturday. In the midst of a July slump that saw the catcher hit .098 this month, Saltalamacchia was given three days off before Saturday's matchup with the Blue Jays -- in part because of the slump and in part because the Red Sox faced lefties for three straight games.
Upon his return, Saltalamacchia made an immediate impact, belting a three-run homer in the second inning. It was Saltalamacchia's 18th home run of the season and wound up being Boston's only runs of the game.
"Two days off was nice," Saltalamacchia said. "Three days off, I would have liked to have played just to get timing down. I'm not going to complain about days off at this time. Any little added extra will help for the long run."
The Blue Jays enter Sunday's series finale with a 6-5 series edge against the Red Sox this season. The teams play six more games against each other after Sunday.
Boston is 3-3 on its current seven-game homestand.