Adam Wainwright (19-9, 2.94) pitches the opener Thursday against the winner of the wild-card game between Cincinnati and Pittsburgh and could also go in Game 5, if necessary.
Lynn (15-10, 3.97) worked six scoreless innings in the Central clincher Friday night against the Cubs. He was 2-0 with a 1.09 ERA his last four starts to end a skid in which he was 0-5 with a 5.44 ERA in eight outings and in danger of getting bumped from the rotation.
He also has pitched the last two postseasons.
"It's an honor," Lynn said Tuesday. "This time of the year you don't care when you start, you're looking forward to it."
Manager Mike Matheny chose Lynn ahead of rookies Shelby Miller (15-9, 3.06) and Joe Kelly (10-5, 2.69), who had stronger overall seasons and Michael Wacha (4-1, 2.78). Wacha threw 8 2/3 innings of no-hit ball against Washington in his last start.
Miller and Wacha both said they hadn't been informed how they'd be used.
Lynn was 9-3 with a 2.82 ERA at home, although Matheny noted that all of the pitchers have done well at Busch Stadium where the Cardinals finished 54-27.
"I think more than anything else is recently how well he's been throwing," Matheny said. "We like the way that he's been rolling; it's a good fit."
The manager would not announce starters for Games 3 and 4, saying "we'll just kind of sit tight" for now.
"We have all the information that you guys have," Matheny told reporters, speaking of home-road splits and other statistical data. "A lot of it has to do with how they've been throwing lately as well as the stats that are there, and there's plenty of stats."
Matheny refused to tip his hand about upcoming roster decisions. Edward Mujica, who had 37 saves before hitting the wall last month, is among those who could be left out.
The manager said the opponent could factor into the decisions.
"We definitely need to see who we play first, before we finalize it," Matheny added.