New York's win, combined with losses by Detroit and Minnesota, assured the Yankees home-field advantage throughout the postseason.
"We got our 10th man," Sheffield said. "It's big in the playoffs, and as loud as these guys get, they're going to pull us all the way through."
Mike Mussina (15-7) tuned up for his start in Game 2 of the playoffs by allowing one run and two hits in six innings, Jorge Posada hit a two-run homer and Alex Rodriguez had three hits for the Yankees, who have a major league-best 97-63 record. Rodriguez also made another overthrow from third base, his 24th error of the season.
Before the game, New York said Johnson has a herniated disc in his lower back, an injury that could prevent him from pitching in the playoffs next week. After being examined by team physician Dr. Stuart Hershon and back specialist Dr. Paul Kuflick, the Big Unit received an epidural injection Friday.
Sheffield, who had wrist surgery June 13, homered for the first time since April 26, ending a span of 68 homerless at-bats. The no-doubt-about-it drive to left off Gustavo Chacin (9-4) gave Sheffield 1,500 RBI.
"(The wrist) is feeling great. I have to thank my doctor and my physical therapist. These guys have been tremendous in bringing me back," Sheffield said. "They told me it's amazing that I'm even playing. It's a testament to wanting to come back and play with these guys."
He is 6-for-26 (.231) with five RBI since returning to the lineup Sept. 22, and he appears to be adapting quickly to first base, a position he had never played in the major leagues before this month.
"He looked a lot more comfortable (at the plate) and at first base, too. I'm pretty comfortable that he can do the job over there," Yankees manager Joe Torre said. "That three-run homer was big for him, just to get that out of the way."
Mussina (15-7) won for just the second time in nine starts since July 30, striking out four and walking none. He gave up Troy Glaus' 38th homer leading off the second, then retired his final 15 batters.
"The counts weren't too tough. It wasn't 3-2 or 3-1 very often," said Mussina, who threw 64 of 88 pitches for strikes. "It's kind of the way you hope to pitch most days you go out there. It was nice."
Mussina was 13-3 with a 3.40 ERA through July, but then went 1-4 with a 4.19 ERA in eight starts going into Friday, getting past the sixth inning just once in that span.
With Johnson's health uncertain, Mussina's outing was a big boost.
"The day I pitch is the only day I can worry about," Mussina said. "We've got guys who can pitch. We've had guys that can pitch all year. If we have to piece it together, then we do. Our chances are really good if he's out there. But he also might not be out there, and we'll have to deal with it if that's the case."
Brian Bruney relieved to start the seventh with a 5-1 lead and walked Aaron Hill with the bases loaded, just the second run off Bruney in 19 2/3 innings since he joined the Yankees. Scott Proctor retired Russ Adams on an inning-ending groundout and pitched a scoreless eighth.
"We had a chance with the bases loaded and one out, couldn't do it," Toronto manager John Gibbons said. "They held us in check all night. Mussina was on. He'll carve you up."
Chacin (9-4), who had been 3-0 in five starts since Aug. 23, allowed five runs -- four earned -- and seven hits in 4 2/3 innings. Toronto dropped into a second-place tie with Boston in the AL East.
New York tied the score in the third when Robinson Cano led the inning off with a single and came home while Derek Jeter was caught in a rundown during Bobby Abreu's double play grounder.
Rodriguez's RBI double in the fifth chased Chacin, and Posada homered off Jeremy Accardo in the eighth.
- Cano went 1-for-4 and dropped one point to .342, one point ahead of Jeter, who went 2-for-4. Minnesota's Joe Mauer was 0-for-4 Friday and leads the AL at .346.
- Johnny Damon went 0-for-3 and is in a 3-for-28 (.107) slide.
- The Yankees drew 52,331, raising their home attendance to an AL record 4,138,605, topping the previous mark of 4,090,692, which they set last year. They have two home dates remaining.
- Chacin is 2-6 against the Yankees.