The Yankees' staff has been cognizant of the stress placed upon relievers in the first month of the season. That was a major reason why Karstens stayed in the game against the Red Sox, throwing five more pitches on what was later revealed to be a fractured right fibula.
If not for a key effort by left-hander Kei Igawa, the Yankees would have had to go to the pitcher that Sean Henn jokingly calls "Johnny Wholestaff," meaning every Yankees reliever might have to get a taste.
"That's the trend," said Henn, a 26-year-old left-hander. "You run the first guy out there and see how long he can go. If he goes two innings, everyone else, you try to get one inning out of everybody. We might use everybody in the 'pen and then bag the next day's starter."
Unfortunately for the Yankees, "Johnny Wholestaff" has been an ever-present option. With starters providing just five quality starts in April, a heavier workload than anticipated was delivered to the relievers. The bullpen logged an American League-leading 97 relief innings heading into May.
"We've put a lot of pressure on our bullpen," Yankees manager Joe Torre said. "The secret to a good bullpen is to not overuse them. We, unfortunately, have done that."
The Yankees used five relievers behind starter Chien-Ming Wang's six-inning effort on Sunday against Boston, the 10th consecutive game in which New York has used five or more arms out of the bullpen. According to the Elias Sports Bureau, that is the longest such streak in the past 50 years, surpassing a nine-game string by the Devil Rays last season.
That makes days off like Monday's even more valuable than usual, as the Yankees attempt to put a skid of eight losses in their last nine games behind them. During that stretch, the Yankees lost five of six to division-rival Boston, with only Igawa's relief effort on Saturday saving them from an even more difficult situation.
"A day when you can just completely relax and not think -- not just your body, but your mind -- it's nice," right-hander Scott Proctor said.
Even though Torre jokes, with gallows humor, that his relievers may be experiencing a ringing sensation in their ears from the flurry of telephone calls to the bullpen, Proctor -- who led the American League with 83 appearances in 2006 -- said he still springs into action, even though his results haven't been ideal of late.
"I never hoped it would be any less," Proctor said. "I want to be out there in every game I can. It shows that [Torre] has confidence in me, and I don't think that's more than I expected."
Fatigue, however, is a valid concern for the bullpen. Proctor has a 5.64 ERA and allowed at least one earned run in three of his last four April appearances. Meanwhile, right-hander Luis Vizcaino has nearly lived up to his nickname, "Daily."
Vizcaino had a 1.08 ERA before coming into an April 19 game against the Indians in New York, when he allowed four runs in one inning and was charged with a blown save. Including the appearance against Cleveland, Vizcaino allowed eight runs in his final seven outings of the month, spanning 5 2/3 innings for a 12.70 ERA.
"[Fatigue is] no problem," Vizcaino said. "When they say pitch, I pitch."
Through 23 games, Proctor and Vizcaino have each made 15 appearances, tying for the Major League lead. Two other pitchers, Brian Bruney and Mike Myers, have been called upon in 14 games.
Sluggish starters and a weary relief corps contributed to the Yankees' recent skid, especially in all five of the losses to the Red Sox. The Yankees held a lead after four innings in each game, but were able to secure just one victory.
Maybe even more strikingly, New York pitchers made a Major League-leading 95 relief appearances through the first 23 games of the season, yet did not record their first save until Mariano Rivera pitched a scoreless ninth inning against the Red Sox on Saturday.
The appearance was Rivera's third save opportunity, but Oakland's Marco Scutaro belted a game-winning home run off the left-field foul pole at McAfee Coliseum on April 15. And the Red Sox capped a five-run eighth inning by defeating Rivera on April 20 at Fenway Park.
Afterward, Torre said that he hadn't been able to get Rivera into a game between those book-ending appearances -- a rare case of a Yankees reliever not getting enough work in 2007.
"As a pitcher, you need to pitch," Rivera said. "This is only the second time this year that I pitched back-to-back games. I need to be out there regularly."
Along the same lines, setup reliever Kyle Farnsworth has rarely made back-to-back appearances, as the Yankees proceed cautiously concerning back spasms that limited his availability in 2006.
"You just have to hang with them," said Farnsworth, who has made 10 appearances and pitched in back-to-back games just once. "Keep on going out there when they call our name, and hopefully do the best we can."
That has left the bulk of the load on others, including Myers -- who no longer seems to be considered simply a situational left-hander -- Henn and hard-throwing Brian Bruney.
"You definitely need to get regular work, in case you get in a sticky situation so you're on top of your game," said Henn, a converted starter and early unsung hero who has posted a 3.00 ERA in 15 innings. "Days off are good, but I also think too many days off can be a problem. But right now, we don't have that problem."
The Yankees' starting staff was never whole to begin with, not with probable Opening Day starter Chien-Ming Wang going down with a strained right hamstring in Spring Training. The player who eventually ended up throwing on April 2, Carl Pavano, is back on the shelf with an injury and just threw his first mound session on Sunday.
But with Mike Mussina scheduled to rejoin the rotation on Thursday, and hot prospect Phil Hughes cutting his teeth on the big-league level, the Yankees' relievers are hopeful that less frantic days are ahead.
But when the phone rings, they'll answer it dutifully, as always.
"I still think we've got the best bullpen we've had since I've been here," Proctor said. "I know a lot of people don't believe that, but I have faith in the guys we have down there right now. We're a close-knit bunch of guys, always pulling for one another, and we've got a lot more ability than people give us credit for."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.