BOSTON -- Red Sox fans were on their feet with two outs in the bottom of the ninth inning on Monday night as Royals reliever Carlos Hernández delivered a full-count 100 mph fastball at the top of the zone to Red Sox second baseman Luis Urías.

A collective groan made its way around Fenway Park when Urías checked his swing and appeared to go all the way around with it. But then cheers erupted when first-base umpire Vic Carapazza declared that Urías did not fully swing, and Urías walked to first to load the bases rather than sending the game to extra innings.

It was the kind of call that can swing a game in either direction.

And it swung the Red Sox's way Monday, as Pablo Reyes followed Urías with a walk-off grand slam that gave Boston a 6-2 series-opening win.

Royals manager Matt Quatraro was livid after Carapazza’s call, immediately coming out to the field to argue while the Royals dugout looked on in confusion. Check swings are not reviewable, so Quatraro could only argue his side before he was tossed -- his second ejection in three days after being tossed Saturday in Philadelphia arguing the strike zone.

“Well, obviously I thought he went,” Quatraro said. “Vic makes the call, obviously he’s got the better angle. But I obviously disagree with that. …

“I can’t think of being much more frustrated than that. He gets the strikeout to move to extra innings. And then he didn’t. I don’t have much else to say about that.”

“It’s a tough job,” Red Sox manager Alex Cora said. “I’m not an umpire, so I’ll leave it at that. But it’s a tough job.”

The Red Sox, who were coming off a three-game sweep by the Blue Jays over the weekend, took advantage of the moment. Rafael Devers had hit a one-out double in the ninth before the Royals intentionally walked Triston Casas to have Hernández face Urías.

Reyes came up the hero.

“I mean … it was a big one,” Cora said. “Let’s see where it takes us, but sometimes games like that kind of get you going and we needed to get going. Even here today was kind of like, ‘eh,’ until the end. We had a tough weekend, we were coming from a tough week and this is a great way to start the week.”

And the Royals, who fell to 36-78 after battling back to tie the game in the seventh inning, thought it took the momentum away from them.

“Nothing really I can explain,” Hernández said through an interpreter. “Just a bad call on the umpire. It’s part of the game. … Just try to do my job. Help the team win. Like I said before, it was a bad call. Changed the outcome of the game.”