His valued right arm healthy and recording Grapefruit League outs with regularity, the Yankees closer has occupied his time by toying with a changeup, which he coyly says may or may not see the light of day this season.
Either way, it has raised a few eyebrows, prompted a few laughs and -- perhaps most importantly -- has achieved swings and misses from opposing batters. Rivera pitched yet another scoreless inning in the Yankees' 5-1 victory over the Phillies on Monday, running his spring total to nine blank frames.
"When I come here, I'm thinking to get ready as quick as possible and throw my innings," Rivera said. "Whatever the results will be, that's fine with me. I don't come here to impress. I do what I have to."
The 37-year-old closer has shown no signs of slowing this spring, reeling off outs with surgical precision. When Rivera allows a baserunner -- as he did Monday -- it has become noteworthy; he has surrendered just four hits and no walks this spring, striking out nine.
"He looks comfortable, and that's the best news for me," Yankees manager Joe Torre said. "He's out there with that changeup and he's not afraid to throw it back-to-back. He looks pretty determined right now."
As the days of Spring Training have whittled down to single digits, Rivera has continued to experiment with the changeup, a pitch that almost seems like an unfair addition for this era's most dominant closer.
"I don't know why," Rivera said. "Just having fun, I guess."
The Yankees have supported the expansion of Rivera's repertoire, cautioning only that he should use it against experienced Major League hitters. Younger players do not provide an accurate enough read of the surprise factor, as some may simply hack at any pitch they can make contact with.
"I just throw it in there and let it float, you know?" Rivera said. "I'm just having a good time."
He's looking A-O-Kei: Making his fifth start of the Grapefruit League season, Kei Igawa appears to have put some early concerns behind him.
The 27-year-old left-hander focused the crux of his effort against the Phillies on improving his changeup, and while he wasn't completely satisfied with his performance, the results were fine. Igawa allowed one run and three hits in five innings, walking two and striking out four to increase his team-leading whiff total to 19.
"I think he's beyond the point of trying to impress people," Torre said. "Now he's understanding what he needs to improve or feel better about going into the season. To me, that was a good step."
The 87-pitch outing was the second straight start of five innings for Igawa, both against the Phillies. His fastball command has improved over the last three weeks, dating back to a wild March 5 debut against the Tigers, and Igawa's slider appears to be a pitch that could garner strikeouts of Major League hitters.
"I've been pitching pretty well lately," Igawa said, through interpreter Yumi Watanabe. "I'm just getting into my style of pitching. ... As I throw more, I'm getting a lot better. There are a couple of things I have to still work on."
Back in the 'pen: Left-hander Andy Pettitte threw 25 pitches in a bullpen session on Monday morning, reporting no further issues with the back spasms that have kept him off the field for a week.
"I didn't want to feel anything, and I didn't," Pettitte said. "This was as good as I could expect."
The bullpen session was the first of two that the 34-year-old Pettitte is projected to throw this week, with another tentatively scheduled for Wednesday.
That would permit Pettitte to throw in game action on Friday, a performance which Torre said would likely come in a Minor League game. Such an arrangement would save Pettitte a trip to Joker Marchant Stadium in Lakeland.
If Pettitte rejoins the rotation on Friday, he would still be unavailable to pitch the season opener April 2 at Yankee Stadium. The assignment could go to either Carl Pavano or Igawa, with Pavano widely considered a front-runner.
"We've got to remember that there are 162 games," Torre said. "It's the long haul that we're concerned about. Whenever we're comfortable that [Pettitte is] ready to take the ball and go out there, that's when it'll be."
Good news on Karstens: The Yankees received "normal" reports on Jeff Karstens, the best possible outcome of a battery of examinations on the hurler's tight right elbow.
Karstens, 24, left his start Sunday against the Tigers after just two innings. He was sent for diagnostics later that evening and had a MRI and X-rays taken on Monday, and said that doctors had actually pinpointed the triceps instead of the elbow -- a good sign.
"It's just a little stiff," Karstens said. "I don't want to chance it too much. If you keep pushing it and pushing it, you're going to make it worse."
Torre called the news "outstanding." The Yankees plan to re-evaluate Karstens in the next few days, though general manager Brian Cashman was non-committal when asked if Karstens could avoid a stint on the 15-day disabled list.
"We'll see," Cashman said.
Karstens had been in serious competition to serve as New York's fifth starter, especially after ace Chien-Ming Wang went down to a Grade 1 right hamstring strain.
"That's why you try to line up as much depth as you can," Cashman said. "The season's going to start and we'll plug people in."
Yankees honor soldiers: The Yankees honored five injured soldiers returning from battle in Iraq on Monday, part of a pregame ceremony to recognize the Wounded Warrior Project.
Outfielder Johnny Damon, the national spokesperson for the Wounded Warrior Project, presented a $5,000 donation check on behalf of the Yankees. The funds will assist in efforts to bring aid to soldiers injured in battle overseas.
This and that: Ron Villone pitched a scoreless inning against the Phillies' Class A Minor League squad Monday. ... Wang will play catch again on Tuesday, though his timetable remains the same. He is not expected to pitch on a Major League mound until late April. ... The Yankees held organizational meetings on Monday, with the projected pitching staff a major topic of discussion. "It's sort of like a puzzle," Torre said.
Coming up: Pavano gets one more tuneup before the regular season on Tuesday, pitching against the Twins at 1:05 p.m. ET start at Fort Myers, Fla. The right-hander will be opposed by Boof Bonser.
New York is scheduled to use Chris Britton, Sean Henn and Colter Bean in relief. The Yankees plan to bring Bobby Abreu, Melky Cabrera, Jason Giambi and Jorge Posada on the trip.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.