The Steelers (2-0) apparently decided they couldn't wait until the end of the week to determine if Leftwich's still-healing knee would hold up to the stress of playing against the Buccaneers (2-0). Batch has received little work since last season, and Tomlin wanted to give him as much time as possible with the starters during the most important practices of the week Wednesday and Thursday.
Batch certainly has had enough rest time while throwing just 13 passes in regular-season games since 2007.
"It feels good," Batch said Wednesday. "I never imagined it would turn out this way, but here we go."
The Steelers were so crowded with quarterbacks after they reacquired Leftwich from the Bucs in April -- with the intent of starting him during Roethlisberger's four-game suspension -- that the 35-year-old Batch took just a few snaps with backups during voluntary spring practices and training camp.
Because the Steelers didn't plan to carry three quarterbacks while Roethlisberger was out, Batch likely would have been cut had Leftwich not been hurt during the preseason finale.
Now, with Dixon out and Leftwich not quite ready, Batch will make his first start since an essentially meaningless end-of-season game against the Baltimore Ravens in 2007. Before that, he hadn't started since the 2006 opener, which Roethlisberger missed because of appendicitis.
"He's been with the starters, he's been with the second team, he's been with the third team," Steelers wide receiver Hines Ward said. "He understands all the wide receivers. He probably understands this offense better than anybody. We feel good, we've just got to protect Charlie."
Batch's durability was cited by Tomlin as a factor in choosing Dixon to start the season. Still, Batch is known for his intimate knowledge of the Steelers' system and often is seen conferring with Roethlisberger between series to discuss strategy.
"For me, there won't be many more opportunities, Batch said. "You're starting to get up there in years, obviously you're just blessed to be out there in that situation. ... I was a little disappointed because I didn't get that opportunity, but here I am again. All I can do is be ready and go out and take advantage of that opportunity."
Batch played the final three quarters after Dixon was hurt during a 19-11 victory at Tennessee on Sunday, completing 5 of 11 passes for 25 yards. He was sacked twice.
Many teammates expect Batch to be an NFL quarterbacks coach someday soon. First, he has another game or two to play.
"Charlie's been in the game a long time and he knows how to play the game," left guard Chris Kemoeatu said. "I don't think we will have any problem with Charlie stepping in there."
To Batch, the biggest challenge -- especially after playing so little for so long -- is growing accustomed again to game speed. He has thrown 1,472 passes in the NFL, but just 146 over the last nine seasons, an average of 16 per season.
"You try to simulate as much as possible on the practice field," he said. "I think for me, going against our defense every week, it kind of allows me to go out there and work the pocket a little more in practice and be able to shift that into an actual game situation."
While Batch is replacing Roethlisberger, his off-the-field reputation is much different from that of the Steelers' troubled star. Batch runs a much-praised youth sports program -- the Best of the Batch -- in his hometown of Homestead, a few miles from Pittsburgh, that has been modeled by much-larger cities.
The Associated Press contributed to this report.