With the Rays' defeat of the White Sox, Boston fell to 5 1/2 games behind Tampa Bay in the American League East.
Following Saturday's loss, Lester (12-5) gathered a laundry list worth of negatives from his start.
"Nothing was really working," he said. "I was rushing through my delivery, not a good tempo. When I did get the ground balls that I needed, they weren't at people. It just wasn't my day. Basically everything you don't want to do, I did today."
Toronto (67-62) was able to set a tone for the game in the first inning, when center fielder Vernon Wells hammered the first pitch he saw from Lester off the facing of the stadium's second deck for a two-run home run to open the scoring.
The home run was a sign of things to come, especially given that Lester considered his pitch to Wells as one of his best during the game.
"I think it probably was the best pitch I threw all day," said Lester. "It was the only ball that was down. Actually, I threw it to my target and he did a good job of hitting."
Following Wells' first-inning shot, the Jays were able to score one run in the second inning and another four off of Lester in the third. In total, the left-hander was rocked for seven runs on eight hits over just 2 1/3 innings. The seven runs he allowed also tied a career high, which he set on Aug. 18, 2006, against the Yankees.
"Today, he just seemed a little flatter up in the zone," said Boston manager Terry Francona. "He made some mistakes, and on top of that, it seemed like every ball today found a hole."
Reliever Chris Smith, who was brought in to rescue Lester, did not fare much better, as he allowed four runs over his 2 1/3 innings. Overall on the afternoon, the Jays combined to hit .421 (16-for-38) against Red Sox pitching.
Wells, who added another homer later in the game, finished the day 4-for-5 with three RBIs. He was one of six Toronto players to collect an RBI.
What may be a cause for concern for the Red Sox is that their pitching staff has posted a 7.81 ERA over the past six games. Included in those contests are three games in which the opposing team has scored at least 10 runs.
Francona was asked if this worried him.
"It didn't help us win today," he replied. "If it doesn't get in the way of us winning tomorrow, then no. If Dice-K comes out and pitches the way he's supposed to [in Sunday's game], then it doesn't matter what happened last week."
In Saturday's affair, though, the pitching did not perform and the offense did not help matters at all. Boston's hitters could not counter the Jays with a sole run, as they were handcuffed by Toronto starter Jesse Litsch (9-7). The right-hander allowed just three hits over his six innings.
"He got off to an early lead, which can help a guy settle down," said Sox left fielder Jason Bay. "He did a good job of throwing fastballs and just keeping guys off balance. It was a pretty good start."
Following Litsch, the Jays' relievers were able to continue the trend by providing three scoreless innings, allowing just one hit.
"I guess it's just one of those days," said Lester, summing up the feeling inside the Boston clubhouse. "You have them every now and again. You just have to forget about it, wash it down the drain and come back tomorrow."
With just 33 games left in the season, it is important for the Red Sox to put together a streak if they hope to secure a playoff spot. With Tampa Bay's win over Chicago, the Red Sox kept pace and stayed a half-game ahead of the White Sox in the Wild Card race.
The Red Sox are still very confident, though, according to slugger David Ortiz.
"We're fine," he said. "We go through the same [stuff] every year, and at the end of the day, we'll be taking another [World Series] ring."