Zimmermann looks to possibly lead the Nationals to their first division title while Lohse tries to help the Cardinals move closer to clinching the NL's second wild-card spot Saturday night at Busch Stadium.
Although Washington (95-62) was on the wrong end of a 12-2 drubbing in Friday's opener, the franchise's magic number for winning the East was reduced to two when Atlanta lost to the New York Mets. The Nationals lead the Braves by four games with five to play and could wrap up the division Saturday.
"The Braves finally lost a game this month, so I guess we can take that as a positive," Adam LaRoche said.
The Cardinals (85-72), winners of nine of 11, are also on the cusp of a clincher, with a magic number of three over Los Angeles to get back to the playoffs for a chance to defend their World Series title.
"I think our team's coming together nicely,'' said Adam Wainwright, Friday's winning pitcher. "We've been playing good ball for the last few weeks and we're going to be a very dangerous team if we get in there. When we get in there.
"Hopefully it happens sooner rather than later.''
Allen Craig matched his career best with four hits to go with two RBIs Friday, while Yadier Molina hit a two-run home run.
Those two have played a big role in St. Louis' surge, with Craig batting .395 with nine RBIs in his last nine games, and Molina hitting .333 with three homers and eight RBIs in his last nine.
With Friday's outcome in little doubt, both managers began taking out their starters for rest.
St. Louis' Matt Holliday was removed in the sixth inning, but that came after he was hit by a pitch on the left elbow. The team said Holliday had a contusion and was day to day.
Cardinals third baseman David Freese missed his fourth straight start with a sprained right ankle, and it's unclear if he'll be ready to return Saturday.
Runs could be at a premium as the series continues with Lohse (16-3, 2.77 ERA), owner of the NL's third-best ERA, going up against Zimmermann (12-8, 2.90), who has the league's seventh-best ERA.
A pitchers' duel never materialized the last time they opposed one another, however.
Lohse gave up a season-high eight runs - five earned - and nine hits over 5 2-3 innings Sept. 1 in the nation's capital, while Zimmermann was shelled for a career-worst eight runs and eight hits in a season-low 3 2-3. Holliday and Freese each homered off Zimmermann, while LaRoche and Danny Espinosa homered off Lohse in a game the Cardinals rallied to win 10-9.
In four starts since, Zimmermann is 3-0 with a 2.19 ERA, yielding two runs or fewer in each.
Lohse, meanwhile, is 2-1 with a 2.49 ERA in his past four. Against the Chicago Cubs on Sunday, he allowed three runs and five hits in six innings of a 6-3 victory, establishing a career high for wins.
The right-hander is 3-0 with a 0.41 ERA in three home starts against Washington since arriving in St. Louis in 2008.
Zimmermann hasn't fared well at all against the Cardinals, going 0-2 with a 10.71 ERA in four career outings.