BOSTON - If there was one consensus surrounding the Yankees when they left spring training, it was that they would have one of the best bullpens in baseball.

But one this dominant?

That has caught even the most optimistic observers by surprise.

"Yeah, a little bit," Joe Girardi said before Sunday night's game against the Red Sox. "And it's been really spread throughout, too. A lot of times in a bullpen, you might have three or four guys going well, maybe five, and you might have one struggling or just doing OK. You look at all of our guys, they've all been doing extremely well."

That, of course, is an understatement.

The seven-pitcher unit entered Sunday night leading the majors with 101 strikeouts in 872/3 innings -- 25 in 142/3 innings by Dellin Betances, who struck out all four batters he faced Saturday -- and a .157 opponents' batting average. They ranked second in baseball with a .485 opponents' OPS and were third with a 1.64 ERA.

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It was even better in the 15 games going into Sunday night. The relievers posted an MLB-best 0.74 ERA and .111 opponents' batting average.

"For a two-week period, it's been about as good as it could be," Girardi said. "I don't imagine it could be much better."

Much of the credit for the performance has gone to Betances, who entered Sunday night not having allowed an earned run this season, and Andrew Miller, who was unscored on in 121/3 innings and was 9-for-9 in save chances.

But Miller, second in the bullpen with 21 strikeouts, echoed Girardi, saying the focus on just himself and Betances doesn't capture the full picture.

"I think top to bottom we're pretty good," Miller said. "There's not that big of a gap between 1-2 and 3-7. We've got a good group of arms and it's just about handing the ball to the next guy and putting a zero up."

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Betances said regardless of how deep a starter goes, collectively the bullpen is confident it will take care of business.

"We're a fearless group down there," Betances said. "No matter who's out there, we believe we can get the job done. We feed off each other."

The Royals made it to the seventh game of the World Series last season with a lockdown bullpen, one that manager Ned Yost firmly believed would carry his team if handed a lead after six innings. More often than not, he was right.

"That's the environment we're trying to create," Brian McCann said. "We've got arm after arm coming out of that bullpen. And we're bringing out [quality] stuff. A lot of uncomfortable at-bats late in ballgames."

Entering Sunday night, the Yankees were 10-1 with the lead after six innings, 11-0 when leading after seven and 15-0 when leading after eight.

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There are a variety of reasons the Yankees, winners of 12 of 15 going into Sunday night, rebounded from a 3-6 start, none bigger than the efforts of the bullpen.

"When we were 1-4, we looked about as bad as we could look," Girardi said. "It's been a big turnaround, but I thought our guys were capable of doing it. With the way our bullpen is, if we get in close games, you feel pretty good about the score staying relatively the same."

Notes & quotes: It didn't look as if it would, but Sunday night's game also came down to the bullpen. The Yankees went ahead 8-0 in the top of the sixth, but the Red Sox scored five runs after two were out in the bottom of the inning to get back in the game. Mark Teixeira hit a two-out, two-run homer to left-center off righthander Joe Kelly in the first inning, McCann added a two-out, two-run double and scored on Carlos Beltran's double in the third and Brett Gardner hit a three-run homer off lefthander Craig Breslow in the sixth. David Ortiz had a two-out RBI double and scored on Pablo Sandoval's single in the bottom of the sixth as the Red Sox knocked out Yankees starter Adam Warren. Mike Napoli then hit a three-run homer off Esmil Rogers.

Brendan Ryan, who started the season on the disabled list with a right calf strain, was scratched from a rehab start in Tampa on Saturday because of a hamstring injury that Girardi said will keep him out for at least a week.