"His at-bats are as good as anyone on the team," manager Bobby Valentine said. "Everyone knows he can hit a fastball and he hits a breaking ball. ... He's a good player."
Jarrod Saltalamacchia led off the ninth with a double to right field and later advanced to third after Mike Aviles flew out to center.
With two outs and the go-ahead run 90 feet away, Ciriaco hit a double down the left-field line to score Saltalamacchia with the game-winning run.
Down 2-1 in the count, Ciriaco turned on an 86-mph changeup from Steve Delabar and drove the ball with authority to increase his average to .300, while driving in his 18th run of the season.
"He always finds a way to get on base, always finds a way to get himself in scoring position and does the little things right, which is what you need to do to win ballgames," Saltalamacchia said about Ciriaco.
"That's why he's still here and that's why he's going to be here for a while."
The rookies have been the difference so far this series. On Friday, it was Mauro Gomez who hit a big two-run triple -- the first of his career -- to lead Boston to an 8-5 victory.
Craig Breslow worked the eighth to earn the victory and Andrew Bailey closed things out in the ninth for his fourth save of the season.
"That's good pitching, really good pitching," Valentine said, then added about Bailey. "I wish I had him all year."
The late-game heroics overshadowed what was a pitchers' duel between starters Clay Buchholz and Carlos Villanueva. Both pitched strong enough to win, but neither factored into the decision.
Buchholz, who went 8 2/3 innings in a loss to the Blue Jays his last start, recorded his eighth quality start in his past 11 outings and went seven innings for the 10th time in his past 11 starts.
He put the Red Sox in an early 1-0 deficit, but Cody Ross evened things up in the second, leading off the inning with a homer, his 21st of the season, to left field off Villanueva. Of Ross' 21 homers, 11 of them have either tied the game or given Boston a lead.
Buchholz was given a 2-1 lead when Saltalamacchia hit an RBI single to center field in the fourth.
But the lead didn't last for long. Buchholz surrendered a leadoff single to Anthony Gose in the fifth, and he later came around to score on a sacrifice fly by Adam Lind to even things up at 2.
After that, both teams stayed off the board until the ninth inning.
Buchholz allowed two runs -- one earned -- on four hits, while walking five and striking out five.
"It feels good. It's a shame it didn't happen at the beginning of the season when I wanted it to, or expected it to," Buchholz said about his run of success. "That's why this game is humbling; you can go out there and feel great and give up six runs, or you cannot have your best stuff and get through seven innings.
"I feel good about it, but I wish the whole scenario was a little bit different for the team."
The only thing Buchholz struggled with was his control, as the five walks matched a season high -- three of them, including an intentional walk, were to designated hitter Edwin Encarnacion.
"Buchholz was great," Valentine said. "He threw the ball exceptionally well. He's really pitching with confidence and all of his pitches were working for him."
Valentine felt the key for Buchholz was the ability to keep his fastball down in the zone, which Saltalamacchia said led to a lot of swings even when he was slightly missing.
Buchholz felt he was leaving too many balls up early in the game and made a point the rest of the way to pound down, which he said was also necessary because home-plate umpire Bob Davidson had a low strike zone.
The 28-year-old Buchholz continued his strong run of success against Toronto, lowering his ERA to 2.52 in 15 career games, 14 of which have been starts. He has been even better at Rogers Centre, where he is 6-2 with a 1.67 ERA over nine starts.
Villanueva, meanwhile, was perhaps even better. Besides Ross' homer, the right-hander allowed just three singles and worked into the eighth inning for the first time this season. He went seven-plus frames and allowed two runs while walking two and striking out six.
"I'm glad I was able to keep the team in it," said Villanueva. "Go deep into the game. It was nice being out there for the first time this year in the eighth inning. It's tough. Two tough losses in a row, and the bottom line is if we don't win the game, then I'm not happy."
Saltalamacchia added that Villanueva keeps opposing teams guessing and does a good job throwing his offspeed pitches for strikes.
"He never gave in," Saltalamacchia said. "He makes his pitches. I don't know what the ratio was, but he didn't [throw] a lot of fastballs unless he was behind in the count. When he did ... [it was in] the right place. He's a good pitcher."