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After getting little help from their closest pursuer, the Washington Nationals can now clinch the franchise's first division title in over three decades all by themselves.

A win Sunday against the St. Louis Cardinals would give the Nationals the NL East title and also keep them ahead in the race for the league's best record.

Already assured of the first postseason appearance in the nation's capital since 1933, Washington (96-62) reduced its magic number for the division title to one with a 6-4 victory in 10 innings Saturday night. Michael Morse hit a first-inning grand slam that was upheld by a video review and Kurt Suzuki delivered a two-run double in the 10th.

That would've been enough to give the Nationals the franchise's first division crown since Montreal won the East in 1981 if Atlanta had lost, but the wild card-leading Braves beat the Mets for their 11th win in 14 games.

"We showed a lot and we showed what good teams do, and that's bounce back and battle through adversity," said closer Drew Storen, who blew his first save in four chances. "So it's ours for the taking tomorrow.

"We're going to be ready, lace it up and let's get it done."

The victory moved Washington one game ahead of Cincinnati in the race for the NL's best record and home-field advantage throughout the playoffs.

With only their second win in the last 13 games in St. Louis (85-73), the Nationals improved to 6-17 there since the 2005 season.

The Cardinals' magic number for locking up the second wild-card spot remained three after they had a five-game home win streak snapped and the Los Angeles Dodgers beat Colorado.

"They're all tough right now, every game," manager Mike Matheny said. "The guys did a great job fighting back, but still it's all about the wins. We got close."

St. Louis native Ross Detwiler (10-7, 3.28 ERA) will try to pitch Washington to a historic win Sunday.

The left-hander had been 3-0 with a 2.43 ERA in his previous five starts before he allowed five runs over five innings in a 6-3 loss at Philadelphia on Tuesday. He surrendered two homers in the defeat -- his first since Aug. 22 -- after yielding only three in his previous eight outings.

Detwiler, who has never faced his hometown team, has one win in his last 11 road starts and he could face a stronger Cardinals lineup if third baseman David Freese returns after missing four games with a sprained right ankle. Freese, who took batting practice both Friday and Saturday, has a career-high 20 homers and ranks fourth on the team with 79 RBIs.

"I felt pretty good running, making cuts and turning," Freese told the team's official website. "I'm close."

St. Louis will send red-hot Lance Lynn (17-7, 3.69) to the mound hoping he can continue his resurgence. Since returning from a stint in the bullpen, the right-hander has won all three of his starts, compiling a 0.93 ERA while striking out 21 and walking six.

"It got me back in sync," Lynn told the team's official website about his time as a reliever. "I was a little out of sync and everything was snowballing on me. I went down there and worked on what I needed to work on to getting back to being successful. It has worked so far."

He was outstanding again Monday in a 6-1 victory at Houston, allowing one run in seven innings with nine strikeouts and two walks.

This will be Lynn's first career start against the Nationals after giving up four runs over two innings in a pair of relief appearances earlier this season.