Rivera was clipped by a stray baseball from the Red Sox bullpen on Sunday, startling him while he was stretching during the eighth inning. The ball struck his interlocked hands and robbed him of all sensation in his right pinkie finger just prior to his entrance into a two-run game.
"That thing was numb," Rivera said. "I didn't have feeling for the whole game."
Neither manager Joe Torre nor general manager Brian Cashman had any idea that Rivera was ailing until Monday. And while he claimed that it didn't have any effect on his performance -- his pinkie barely touches the ball on a cut fastball -- Rivera walked two in the inning and allowed a run before finally slamming the door.
"I would have been more freaked out if I was told before he was coming in that he can't feel his finger," Cashman said. "It would have made the ninth inning worse."
Rivera said that the pinkie was sore a day later, but nothing worse. He was available to pitch on Monday night, though for only one inning.
More than anything, mystery lingers regarding exactly how the episode occurred. Rivera said that he originally thought a fan had thrown a ball at him before realizing that the angle from which it came would have made such a feat impossible. Because of where he was standing, Rivera realized that there was only one possible origin for the ball.
Boston's Fenway Park boasts a unique architectural layout in which the bullpens -- far removed from each other in most ballparks -- lie end to end in right field. They're separated by only a low wall, meaning that one stray pitch could easily jump to the other side.
Regardless, Rivera said that he didn't suspect any foul play, while Cashman said he wasn't interested in contacting the Red Sox to determine the exact cause.
"It can happen anywhere," Rivera said. "I know they didn't do it on purpose."
Matsui drained: Hideki Matsui said he's been feeling "fatigued" during the stretch run, which is part of why he believes he's been mired in a September slump.
Matsui entered Monday hitting only .125 in September, dropping his overall average to .289, its lowest point in more than a month. More concerning, his power has all but disappeared. After hitting 13 home runs in July, Matsui has managed just two long balls since, and none in September.
"I think fatigue is certainly one of the factors," Matsui said through his interpreter.
Matsui has been bothered by a bad knee all season, but he said that this most recent slump has nothing to do with the injury. Torre noted that Matsui has been back on his heels while swinging, which in turn has affected his balance at the plate.
"Physically, I feel fine," Matsui said. "Certainly the results aren't there, but swing-wise, I feel better out there."
First in line: After a strong performance on Sunday night in his first start since fracturing his right wrist, Doug Mientkiewicz may just have wiggled himself into more consistent playing time.
Mientkiewicz finished 2-for-3 in Boston with a run scored and a series of sparkling defensive plays. With Andy Phillips out for the season and Jason Giambi not as strong defensively, Mientkiewicz should see more time at first base down the stretch. He was in the starting lineup again on Monday.
"I think [Sunday] was a big game for us to see, and he certainly took advantage of it," Torre said. "He certainly has to be added to the mix."
Torre made Monday's move with one eye toward Giambi, whose right elbow was still ailing after he was hit by a pitch on Saturday. Giambi was available to pinch-hit on Sunday -- which he did -- but not to field, and his status remained unchanged a day later. He was in Monday's lineup as a designated hitter.
Fresh faces: The Yankees added two new players to their roster on Monday, recalling both Tyler Clippard and Chase Wright from Double-A Trenton. The two come fresh off the Thunder's Eastern League championship, which the team clinched on Saturday night.
"In the Minor Leagues, you don't have the World Series, but that was our World Series," Clippard said. "To accomplish what you set out to do, there's no better feeling."
Clippard, 22, made six starts for the Yankees in May and June, going 3-1 with a 6.33 ERA. Wright, 24, made just two starts in April. He won the first of them, but he is perhaps best remembered for serving up four consecutive home runs to the Red Sox in his next outing.
Neither is expected to play a prominent role for the remainder of this season, though Clippard was quick to note that his experiences on the winning team in Trenton have colored his perceptions of what it takes to succeed in New York.
"I think it helps," Clippard said. "Any time you can play a meaningful game, it will help. It's a little different feel when it's the playoffs. It's nice to have that, and it's good to have that experience under my belt."
Pitching prospects Alan Horne, Jeff Marquez and Dan McCutchen also joined the Yankees on Monday to work out with the team, though they won't be added to the active roster. It's part of an experiment that began with Clippard and Phil Hughes last season and something that Torre was eager to repeat.
Movin' on up: With a single in the first inning on Monday, Derek Jeter tied Bernie Williams for fourth on the Yankees' all-time hit list with 2,336. Jeter recorded a double in the eighth to claim sole possession of fourth place on the list.
Jeter's total now trails only those of Lou Gehrig, Babe Ruth and Mickey Mantle. Gehrig has held the current Yankees record of 2,721 hits for 68 years, though at Jeter's current rate, he'll shatter that mark at some point in late 2009.
Bombers bits: Roger Clemens is on track to start Sunday's series finale against the Blue Jays, with the Yankees effectively employing a six-man rotation. Chien-Ming Wang and Ian Kennedy will start the first two games of the series. ... Melky Cabrera received a routine day off on Monday. Cabrera has just one hit in his last 27 at-bats, and Torre joked that his brain was "scrambled eggs." ... Shelley Duncan was apologetic regarding an episode in Boston in which a fan took offense to a comment he wrote in jest next to his autograph. "It's just me," Duncan said. "I'm out here having fun with people."
Coming up: On Wednesday night, Mike Mussina (9-10, 5.28 ERA) will make his second start since his recent two-week hiatus from the rotation. He'll oppose Orioles right-hander Jon Leicester (2-1, 6.32 ERA) at 7:05 p.m. ET.
Anthony DiComo is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.