Mussina limited Baltimore to three singles over seven innings, Mientkiewicz hit a three-run homer and the Yankees beat the Orioles 12-0 on Tuesday night to inch closer to the first-place Red Sox.
"I felt I could do whatever I wanted to do whenever I wanted to do it," Mussina said. "You don't have many days like that."
New York, which has won 11 of 13, closed within 2½ games of Boston in the AL East, the Yankees' smallest division deficit since before play on April 21. They also opened a 4½-game lead over Detroit in the wild-card race.
"We've still got work," said manager Joe Torre, whose team is a season-best 23 games over .500. "We cannot allow ourselves to get caught up in what people will assume is a foregone conclusion."
The Yankee Stadium crowd roared when Boston's 4-3 loss at Toronto was posted on the scoreboard in the bottom of the eighth inning. By then, New York had scored in double digits for the fourth time this month and the 21st time this season.
Mientkiewicz also had an RBI single, and Melky Cabrera and Hideki Matsui drove in three runs apiece for the Yankees, closing in on their 13th consecutive playoff appearance. Derek Jeter added three hits.
"The Yankees are on a roll right now," Orioles manager Dave Trembley said. "They're a real good team. They're playing well."
Ramon Hernandez singled twice and Miguel Tejada reached on an infield dribbler in the seventh for Baltimore's only hits off Mussina, who improved to 10-6 against his former team. He allowed only one runner to reach second.
"He's got a lot of life right now," Torre said. "It's really good. Throwing a lot of strikes."
Mussina also helped himself with two nice defensive plays. The six-time Gold Glove winner bounded off the mound to grab Tike Redman's grounder in the first inning and start a 1-6-3 double play. He knocked down Nick Markakis' hard comebacker in the seventh and threw him out at first.
Tejada reached after Markakis was retired and went to second on Kevin Millar's grounder back to Mussina. With the Yankee Stadium crowd yelling "Mooose," the right-hander threw a called third strike past Aubrey Huff to end the inning.
Mussina (10-10) was dropped from the rotation in late August after allowing 19 earned runs over 9 2/3 innings in three consecutive losses. He made one relief appearance after that, his first ever in a regular-season game.
"This has not been the easiest year," he said. "Certainly not what I was looking forward to or planning for, but it is what it is. I make my living out there pitching and I have to keep doing it.
"I wasn't ready to be the pitcher that I was there for a while. I wasn't ready to do that yet."
Mussina struck out six, walked one and has thrown 12 2/3 scoreless innings over two outings since his starting spot was restored. He has won at least 10 games in an AL-record 16 consecutive seasons.
"He was as good as he has been in a few years," Millar said.
Orioles right-hander Jon Leicester matched Mussina through the first three innings but ran into trouble in the fourth. New York batted around and scored six times, getting the type of fortunate bounces that help teams reach the postseason.
"I was just pitching the way I wanted to pitch, but the hops just weren't going my way," Leicester said. "It's a tough Yankee lineup, and things happen in a hurry."
Jeter led off with a single and Bobby Abreu followed with a liner that glanced off third baseman Melvin Mora's glove and went into left field for a double, putting runners on second and third. Alex Rodriguez struck out but Matsui's hard grounder skipped past first baseman Huff for a two-run double.
One batter later, Robinson Cano grounded a perfectly placed RBI single up the middle and Mientkiewicz followed with a drive to right for his first homer since May 23 against Boston's Curt Schilling.
Mientkiewicz was activated from the disabled list Sept. 1 after missing much of the season with a broken right wrist. He is batting .462 (6-for-13) with six RBI since he rejoined the club.
"I'm just trying to stay within the game and whatever's needed at that given moment, just sort of do it and just do your job," Mientkiewicz said.
Leicester (2-2) allowed six runs and six hits in four innings in his first career appearance against New York.
The Yankees also batted around during their five-run seventh. Mientkiewicz singled in a run and Cabrera drove in two with a base hit, ending a 1-for-29 skid.
Mientkiewicz had four RBI for the first time since he did it for the Mets on April 21, 2005, at Florida.
- Matsui said he hasn't had X-rays or an MRI exam on his ailing knee but that he will at the end of the season. Matsui has no idea whether he will need surgery.
- Orioles RHP Daniel Cabrera dropped his appeal and started serving his six-game suspension for throwing at Boston's Dustin Pedroia this month. Trembley said Cabrera's next start will be Monday against Kansas City.
- San Diego's Greg Maddux (19 seasons) is the only active player with a longer streak of seasons with 10 or more victories, according to the Elias Sports Bureau.