BOSTON -- The moment kept building and building, and at one point you could almost feel something special was going to happen.
In an at-bat that will be hard for anyone to top for the rest of the season, Red Sox star Mookie Betts battled Blue Jays starter J.A. Happ for 13 pitches and smashed a 3-2 offering over the Green Monster and onto Lansdowne Street for a grand slam that sent Fenway Park into a state of eruption.
With that one swing in the bottom of the fourth, Betts turned a 2-1 deficit into a 5-2 lead for Boston, which went on to win its 10th game in a row, 6-4.
The slam brought the normally low-key Betts into a state of delirium. As he reached first base, he twisted, turned and shouted with excitement toward his dugout and nearly lost his balance.
• Betts stumbles to first in excitement after slam
"Obviously, everyone was excited. A big moment in the game kind of swung everything around. It was definitely fun," said Betts. "Since I've been in the big leagues, that's probably the most excited I've been."
Why so much emotion?
"It was probably the at-bat, how the whole inning was going, everybody was kind of waiting for something to happen," said Betts. "[Happ] was tough. But we kind of showed and we battled, that was the main thing. I was just looking at the dugout, excited. A good time to show some emotion."
The accomplishment was indeed a rare one.
This was the first time a player hit a grand slam in an at-bat of 13 pitches or more since Gary Scott did so for the Cubs on the 13th pitch against Philadelphia's Kyle Abbott on April 20, 1992.
It is also the longest at-bat that ended in a home run by any Red Sox player since at least 1988. Dustin Pedroia (May 27, 2007) and Adrian Gonzalez (April 6, 2011) both homered on the 12th pitch of an at-bat.
"In that moment you have to stay focused, especially with that guy on the mound," said Betts. "I was able to foul some of those pitches, and I got pretty comfortable once I was able to foul that fastball up. We were swinging through it all day."
Beyond tipping his cap, there wasn't a whole lot Happ could do.
"It was a great at-bat by him. All the credit to him," said Happ.
Some fortuitous things had to happen for Betts to be able to be in that spot. Earlier in the inning, there was a bang-bang play at second in which Xander Bogaerts was initially called out, but the call was overturned after a challenge by the Red Sox.

And on the fourth pitch of Betts' at-bat, Jays first baseman Justin Smoak raced back for a foul ball and dropped it.
"You look at it, two great competitors. He just kept fouling it off, nicked a couple to stay alive," said Jays manager John Gibbons. "It was a great battle. Betts, he could be an MVP this year. It's exciting to watch."

Happ started the at-bat with six straight fastballs, then mixed in two changeups and another fastball, and the count was still just 1-2. Betts took a slider in the dirt for ball two. He then fouled off a 95.6-mph fastball. On the next pitch, Happ unleashed a two-seamer in the dirt that nearly got far enough away to be a wild pitch.
With the count full, NESN analyst Dennis Eckersley exclaimed to his audience, "It's time to party."
Betts launched the next pitch into the night, belting a low, 95.2-mph heater with an exit velocity of 108.3-mph and a projected distance of 407 feet.
It was the 23rd homer of the season for Betts, and his fourth career grand slam.
Boston's dugout buzzed as the at-bat continued. Manager Alex Cora, who worked an 18-pitch at-bat as a member of the Dodgers for a homer against Matt Clement on May 12, 2004, took a keen interest as he watched Betts grind it out.
"We were guessing pitches," said Cora. "I told [bench coach] Ron [Roenicke], 'changeup here,' and he's like, 'fastball up,' and we both were wrong -- it was a fastball down. He kept fouling off tough pitches, and you can see he was gaining confidence at the plate, and you expect good things when he's at the plate, obviously. "

After not hitting a grand slam in 2017, the Red Sox have hit eight this season. Two of them have come from Betts, who is having a monster season.
"I think the most important thing is, it wasn't just me that at-bat," said Betts. "We had an overturned call, the walk, [Eduardo Nunez] hustling, beating out that hit. It was a collection of everything, and then I was able to get a good pitch to hit."