Amidst the revelry of the moment, as decoy Joba Chamberlain dashed onto the field to distract Posada before A.J. Burnett smashed his whipped-cream special onto the catcher's face, New York's ninth win in 10 games had a tempering of enthusiasm.
Yankees starter Chien-Ming Wang left the game in the sixth inning due to injury and watched the conclusion from the clubhouse, having departed for an MRI exam that showed a right shoulder strain and bursitis before returning in time to see Posada's at-bat.
"The win is great," Yankees manager Joe Girardi said. "Obviously, you don't ever want to lose anyone. I thought today was probably his best start -- that's the unfortunate thing."
Wang had worked 5 1/3 innings before an 86 mph sinker raised a red flag in Posada's eyes, drawing the catcher out to the mound. Within seconds, Posada was calling to the bench and summoning Girardi with assistant trainer Steve Donohue, and Wang's outing -- and perhaps his month -- was over.
One pitch earlier, Wang had felt tightness in his pitching shoulder as he left one up to Adam Lind, belted over the right-field wall for a two-run homer. That shot gave the Blue Jays a 4-3 lead at the time, with Wang permitting four runs on six hits, walking one and striking out one.
"He was spotting all of his pitches and getting a lot of ground-ball outs," Posada said. "Even the base hits were ground balls. The only pitch he left up was the home run to Lind, but other than that, everything was down."
Alex Rios stroked a two-run double in the second inning and added a run-scoring single in the sixth off Dave Robertson, who relieved Wang and had unlimited time to warm up because of the injury.
That began a successful sequence of Yankees relievers who held Toronto the rest of the way as New York mounted a comeback against an ineffective Roy Halladay, who served up three home runs in a game for the first time since April 6, 2008, against Boston.
The third of those came off the bat of Johnny Damon, who slugged a game-tying two-run blast to right field in the seventh inning. The shot, Damon's 16th, improved his lifetime numbers against Halladay to 30-for-86 (.348).
"There are certain guys that you just see the ball well," Yankees first baseman Mark Teixeira said. "Sometimes you have their number. I didn't know about it until today, when I saw it up on the board, and he was hitting. I thought, 'Man, that's pretty impressive.'"
Halladay ventured seven innings, walking three and striking out three. He was sour in discussing his outing with reporters, wondering if Damon's homer was helped by the dimensions of the new Stadium.
"I thought we got in enough, but it wasn't," Halladay said. "It's hard for me to judge those types of things. There are a couple other things I need to look at first, as far as pitches, before I'm going to start getting into that part of it. It was disappointing."
Hideki Matsui also belted a solo shot in the second inning, his 12th, and Posada homered leading off the fourth, part of a five-run, nine-hit attack against the right-hander.
"When he's on, you're not going to score many runs," Teixeira said. "Maybe one or two, if you're lucky. He probably didn't have his best stuff today, but he was still good."
Meanwhile, the Yankees' bullpen managed to string six innings of scoreless relief to preserve the tie after Damon's homer.
Brian Bruney pitched out of trouble in the seventh, inducing Scott Rolen to pop out and Lyle Overbay to line out in leaving the bases loaded, and Phil Hughes hurled another blank inning to run his string to 10 scoreless frames. If the Blue Jays couldn't score, eventually the Yankees would.
"It was just a matter of time, I guess," Hughes said. "Just keep holding on and putting up zeroes."
Mariano Rivera worked the ninth inning around a hit, and Phil Coke tossed two scoreless innings before Brett Tomko shut the Blue Jays down in the 12th inning, setting up Posada's big moment.
Toronto reliever Shawn Camp opened his third frame of work by allowing a double to Teixeira that struck the first-base bag. An intentional walk to Alex Rodriguez followed, and Robinson Cano -- continuing a 0-for-20 span with runners in scoring position -- stunned everyone by bunting on a 3-0 count.
Catcher Raul Chavez scooped the ball and fired it to third base, forcing out Teixeira, who was caught off-guard.
"Missed signs happen," Teixeira said. "Unfortunately, you don't want them to happen in those situations. But Robbie knows he missed it, and I'm sure it will never happen again."
Posada saved the day, drilling a 1-1 changeup into center field as Rodriguez trotted home with the winner. But the Yankees would leave the Bronx wondering what the state of their pitching rotation might be after the holiday weekend, knowing that Wang will not be involved in their mix.
"You're losing a guy who has obviously come a long way from the struggles that he had early in the season," Coke said. "The last two outings, by comparison, have been phenomenal. I'm just glad that we were able to all come together and rally around each other and get the job done."