Mussina limited the Pirates to three hits over five shutout innings at Legends Field, earning the win in the Yankees' 8-1 defeat of Pittsburgh.
Afterward, he said that the game was important because it offered reassuring thoughts not only for Mussina, but also for manager Joe Torre, pitching coach Ron Guidry, general manager Brian Cashman and others in the organization.
"After a while, it's about getting people out and being able to do what I should be doing," Mussina said. "I was frustrated, because I was at that point and I couldn't do it yet. Today was much better."
The 38-year-old right-hander walked one and struck out two, throwing 44 of 67 pitches for strikes. Mussina had been frustrated in his previous three starts by general inconsistency.
He found himself unable to make adjustments on the mound, particularly in throwing breaking balls for strikes, and had compiled a 5.62 ERA by the time he left his last start against Cincinnati on Tuesday.
"Every throw was work before," Mussina said. "Today was more smooth. It didn't take as much out of me. You get to a certain point in Spring Training where it becomes a lot more serious."
That checkpoint, Mussina said, passed sometime during his third start of the spring. Reflecting on that trio of underwhelming outings, he said that he had felt rushed on the mound by his own doing, unable to control game speed past the catcher's signs.
"From the time I got the signal, it felt like a race to throw the ball," Mussina said.
On Sunday, Mussina said there were no such problems, as he made a conscious decision to give himself more time.
He said that he wasn't surprised that he had been unable to pick up where he left off last season -- Mussina was 15-7 with a 3.51 ERA in 32 starts, and the Yankees were 20-12 in those games -- but he seemed satisfied that his command was returning to that point.
"When it's going right, the chances of getting up the next Spring Training and having it feel the same way are very, very slim," Mussina said.
Mussina said that he wasn't bothered by his velocity, which Torre said was similar to the Cincinnati start. After that effort, Mussina estimated that he was throwing about 85 or 86 mph, and said Sunday that it might take until April or May to achieve full speed.
"If I can get the ball where I want to get it, that's more of a battle than throwing it 90 miles an hour," Mussina said.
Out of the running: Mussina said that he didn't believe he would be in consideration to pitch the Yankees' season opener on April 2 against Tampa Bay, instead conceding the battle to Chien-Ming Wang and Andy Pettitte.
"In my mind, it's one of those two," Mussina said.
That said, Mussina does have an opinion. Torre is reserving his decision until after the Yankees' off-day on Wednesday, but Mussina sounds ready to place his bet.
"Wang deserves it. He earned it last year," Mussina said.
An easy day's work: Mariano Rivera made his sixth appearance of the spring on Sunday, though if you blinked, you might have missed it.
The 37-year-old closer needed just six pitches to retire the Pirates in the sixth, throwing four strikes. The effort was so simple, Rivera needed to go into the bullpen to throw 10 more pitches just to get his work in.
"I told him to go work up a sweat," Torre said.
Rivera said he did not throw any changeups in the appearance, a pitch he has been toying with this spring, albeit veiled in semi-secrecy.
Rivera doesn't seem to relish revealing his repertoire, but Torre pointed out that the closer has experimented before. In game situations, Torre said Rivera will attempt to cross up a hitter who has fouled off a succession of pitches by tossing a changeup or a soft slider. He also changes his grip on his fastballs to achieve different movement.
"He's got guts out there," Torre said. "He's got so much confidence in his ability to command the plate that you pretty much leave it to him."
In spring games, Torre said the Yankees have recommended that Rivera only use his "surprise" pitches against experienced hitters. Younger players, Torre reasoned, may simply go up to the plate hacking at whatever they can make contact with.
Phelps keeps rolling: Josh Phelps continues to make the most of his opportunity to make the Yankees' roster as a Rule 5 Draft selection, stroking another two hits Sunday to raise his spring average to .435.
"He's making a case for himself," Torre said. "He's got enough experience where he doesn't speed the game up for himself. When it comes time to make a decision, we'll make one. You hope you make the right decision for the long haul."
Phelps is competing with Andy Phillips to serve as the right-handed-batting complement to Doug Mientkiewicz at first base. If he does not stay on the Yankees' 25-man roster all year, he would be offered back to the Orioles for $25,000.
Think sink: Torre said that right-hander Kyle Farnsworth, who allowed one run, two walks and a hit in an inning on Sunday, has been encouraged to throw his sinker more in game action.
"It gives him another option," Torre said.
Torre said that Farnsworth seems to be more comfortable heading into his second season as a Yankee, and that there are plans to better utilize the setup man for the coming campaign.
"I think he'll be more effective if we get him in a routine where we're not going overuse him," Torre said.
Abreu moved up: Outfielder Bobby Abreu, attempting to return from a strained right oblique, is penciled in to serve as a designated hitter on Tuesday against the Phillies.
Torre said Abreu was moved up after a solid batting practice session on Sunday, and also because the Yankees could better control Abreu's efforts in a home game at Legends Field. The next two games after Wednesday's off-day are road games at National League parks.
"He was turning on the ball [Sunday]," Torre said. "He didn't seem to be hesitant in anything he was doing."
This and that: Right-hander Humberto Sanchez said he threw 25 pitches -- all fastballs -- in a bullpen session. Sanchez will remain in camp to work with Guidry, as he's starting from scratch following right forearm soreness. ... Catcher Wil Nieves is scheduled to play Monday. ... Right-hander Jose Veras will begin throwing Monday after right elbow pain had shut him down.
Coming up: The Yankees travel to Dunedin, Fla., to face the Blue Jays on Monday at 1:05 p.m. ET. Right-hander Jeff Karstens is scheduled to start, with right-hander Tomo Ohka going for Toronto.
Right-hander Scott Proctor and left-hander Mike Myers are scheduled to work in relief for the Yankees. The Blue Jays plan to use right-handers Victor Zambrano, John Thomson and Jason Frasor out of the bullpen.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.