Rubby De La Rosa missed on his pitch to Jose Bautista, and the slugger made him pay for the mistake.
De La Rosa yielded a three-run homer to Bautista in the fifth inning, and the Boston Red Sox went on to a 3-1 loss to R.A. Dickey and the Toronto Blue Jays on Sunday.
Xander Bogaerts had an RBI single for the defending World Series champion Red Sox, who will be officially eliminated from the AL East race with their next loss or Baltimore win.
De La Rosa (4-6) gave up three runs and seven hits in four-plus innings. The right-hander is 0-2 with a 6.20 ERA in his last five starts.
"I thought prior to the fifth inning he used all his pitches well," Boston manager John Farrell said. "He pitched out of a couple of jams, continued to show very good poise. The 2-0 slider to Bautista, unfortunately, nicks him for three runs."
Bautista chased De La Rosa with his 31st homer, a drive over the Green Monster seats and completely out of Fenway Park.
"Yeah, I missed that pitch, tried to throw that pitch like away to him so it's not in the middle," De La Rosa said.
Dickey (12-12) allowed one run and six hits. The knuckleballer was pulled after Mookie Betts' leadoff double in the eighth.
Dickey improved 2-0 with a 1.80 ERA in his last three starts and 4-0 with a 2.23 ERA against Boston this season.
With his pitch dancing in a light breeze, he had a number of Boston's hitters taking big swings that led to many misses, weak grounders or popups.
"As far as a mechanical adjustment, it's nothing that's outstanding," Dickey said of his recent run. "You're always working on your trade."
Adam Lind added three hits for the Blue Jays, who dropped the first two games of the series after five consecutive wins. The Blue Jays were six games behind Seattle for the AL's second wild card coming into the day.
Brett Cecil worked a hitless eighth and Casey Janssen tossed a perfect ninth for his 22nd save.
Boston's hitters had little luck with Dickey early on, collecting just three singles in the first five innings. Jackie Bradley Jr. had the hardest hit ball, a deep drive to the wall in center that was caught with two runners on in the second.
BIG PAPI MAKES `EM SMILE
Red Sox DH David Ortiz is often the last one off the field after taking a number of pictures with fans. "I know it's a part of what I do," he said. "I know people have tons of fun with that. I don't mind. I get caught sometimes in situations where I have to go, but if it's going to take five minutes to make a group of people happy, I just go for it."
Blue Jays: 1B Edwin Encarnacion was the designated hitter after being lifted for a pinch runner late in Saturday's loss. He has been bothered by a right quad injury.
Red Sox: Boston 1B Mike Napoli and INF/OF Brock Holt both were out of the lineup after feeling ill the past couple of days. Holt left Friday's game early and Napoli departed on Saturday. Farrell said both were feeling "much better." Ortiz had a planned day off, but Farrell said they also were "managing that right foot he fouled a couple of balls off recently." Two weeks ago, Ortiz went down hard and left the game after fouling a ball off his foot. He was out of the lineup for two games.
Blue Jays: RHP Marcus Stroman (9-5, 3.83 ERA) is slated to go against RHP Jacob Turner (5-8, 5.54 ERA) on Monday when Toronto opens a three-game series at home against the Cubs.
Red Sox: RHP Joe Kelly (1-1, 3.89 ERA) is scheduled to start the opener of a three-game set in Fenway against AL East-leading Baltimore. Miguel Gonzalez (8-7, 3.38 ERA) gets the ball for the Orioles.
THREE KNUCKLEBALLERS IN THE PARK
Dickey and Boston reliever Steven Wright both mostly throw knuckleballs and pitched in the game. Former Red Sox RHP Tim Wakefield watched from the press box. Wright pitched five shutout innings, allowing two hits.