That doesn't make it any less surprising when it happens.
Rivera blew his first save opportunity of the young season on Sunday, surrendering a three-run home run to infielder Marco Scutaro in the bottom of the ninth inning as the Athletics stunned the Yankees, pulling out a 5-4 victory at McAfee Coliseum.
"I'm shocked," said Yankees manager Joe Torre. "When that can happen with Mo on the mound, you've got to be shocked."
Scutaro reached out and clanged an 0-2 cutter off the left-field foul pole, a pitch that Rivera said was intended to be inside, but zipped back over the plate. As the Athletics spilled out of the third-base dugout to mob Scutaro, Rivera swung his right arm in frustration.
"It doesn't mean anything," Rivera said. "I got two outs, but I couldn't get the third out. That's baseball."
The dramatic defeat sealed a weekend series in which the Yankees lost two of three games to the Athletics, capping an afternoon when New York learned it would also be without two prominent members of its starting rotation.
Before Sunday's contest, right-handers Mike Mussina and Carl Pavano were both placed on the 15-day disabled list with a strained left hamstring and right forearm soreness, respectively.
When the Yankees return to action on Tuesday in New York, they'll take the field at Yankee Stadium behind Chase Wright, a 24-year-old left-hander summoned from Double-A to make his Major League debut against the Indians.
"You can't worry about things that you can't control," Torre said. "The only thing we can control is getting out there and putting our best foot forward. Hopefully, it's good enough."
The outcome spoiled a strong effort from left-hander Andy Pettitte, who suddenly found himself as the most experienced member of the Yankees' rotation when Mussina was shelved.
Making his third start since returning to the club this winter, Pettitte turned in his lengthiest performance of the season, throwing 101 pitches in a seven-inning effort.
"My legs were under me and I felt strong," Pettitte said.
The Athletics touched Pettitte for two runs (one earned) in the first inning, with Derek Jeter bobbling a Shannon Stewart grounder for an error on the first play of the game. Nick Swisher doubled and Bobby Kielty lifted a sacrifice fly to center field before Mike Piazza singled in a run, giving Oakland an early two-run lead.
But Pettitte slammed the door from then on, limiting the A's to just three hits over the next six innings. In total, Pettitte scattered six hits, walking one and striking out four before handing over a one-run lead to Scott Proctor for the eighth inning.
"He gave us everything we needed," Torre said.
Held scoreless and limited to four hits through six innings by Oakland starter Rich Harden, the Yankees finally cracked through in the seventh as the right-hander left mid-inning with a shoulder injury. Alex Rodriguez was Harden's final batter in the six-inning-plus performance, in which the right-hander walked two and struck out seven.
Rodriguez doubled to the gap in left-center field and Jason Giambi greeted reliever Joe Kennedy with a single before Jorge Posada punched a run-scoring double into the corner in left, scoring New York's first run. Robinson Cano and Melky Cabrera followed with successive sacrifice flies to give the Yankees a 3-2 lead.
New York tacked on another run in the eighth as Rodriguez lifted a sacrifice fly off Kiko Calero -- tracked down on a nice running grab by Swisher -- eventually offering Rivera a two-run cushion for the ninth inning as eventual winning pitcher Jay Marshall recorded the last four Yankees outs.
But it would not hold, even as Rivera recorded the first two outs of the frame. Todd Walker singled to left and Rivera issued a walk to Jason Kendall, at which point Posada went to the mound to check on the hurler.
"He said he felt really, really strong, but everything was up," Posada said. "He couldn't bury the cutter."
Rivera worked ahead of Scutaro and got the first two strikes over, but he could not will his cutter in enough on the decisive pitch of the at-bat. Most of the Yankees realized immediately that the swirling winds above the Coliseum wouldn't be strong enough to pull the drive foul, but that didn't do much to mask their surprise.
"More than anything, you realize Mo's a human being," Pettitte said. "I don't think people realize that -- sometimes including us."
The Yankees' six-game road trip to Minnesota and Oakland -- their first of the season -- ends with three victories and three losses, though it would have been difficult to announce to the charter flight that they'd broken even as they winged it back to New York.
Though they escaped the Big Apple's chilly conditions and finally garnered a quality start from their starting staff, the Yankees left Oakland down two starting pitchers, plagued by six errors in the A's series alone and treading an uncertain path ahead.
"We've just got to play better," said Jeter, who has a team-leading six errors. "Our pitching staff has done a great job the last couple of nights, but you can't give good teams extra outs. They're going to capitalize on them."
The only consolation may be that it is still early.
"We're as banged up as you can get," Pettitte said. "Yet we've got a great team still -- we've got a great lineup and our offense is strong. If you give them a chance, they're going to score runs for you. We've just got to tighten the chinstrap right now."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.