ST. LOUIS - This is what the St. Louis Cardinals had in mind when they acquired Brandon Moss at the non-waiver trade deadline.

"That's a long way to go," manager Mike Matheny said after Moss hit a three-run walk-off home run with two outs in the ninth inning for an 8-5 win over the Washington Nationals on Tuesday night.

"I know he's been pressing a bit to show what he can do — and I think we're seeing it."

The NL Central-leading Cardinals have won nine of 10 and lead the division by six games. They've won nine in a row over Washington, coming from behind the last two nights.

After a very slow start since coming from Cleveland, Moss is starting to put things together. All three homers with St. Louis have come in the last six games, and his drive off Casey Janssen (1-4) was his fifth career walk-off.

"I've hit some good ones, but this one definitely is up there just because of where I'm at and how hard it's been to get one here, and the timing of it," Moss said. "Definitely up there."

Moss, who struck out with the bases loaded to end the third, homered to straightaway centre on a 1-0 count. Janssen said it was supposed to be a cutter inside and "I left it up and it was terrible."

Janssen took the loss on Monday, allowing four runs in two-thirds of an inning.

Mitch Harris (2-1) worked the last two innings, allowing two hits. He was among three minor league call-ups Monday.

"Everybody wants to be in this position," Harris said. "It's great to be a part of it."

Ryan Zimmerman homered and Anthony Rendon had a two-run double in a four-run third for Washington.

The Cardinals scored three runs on one hit in the bottom of the third and tied it with two runs on one hit with an error in the eighth.

Both starters lasted just 2 2-3 innings. Nationals rookie Joe Ross gave up one hit but had a season-high six walks and was charged with three runs. Cardinals call-up Marco Gonzales allowed four runs on seven hits with lots of solid contact.

Washington manager Matt Williams said Ross had trouble with his grip.

"He had problems feeling it and throwing it over the plate," Williams said. "No issues physically, he just couldn't command it."

Gonzales, who was 1-4 with a 5.20 ERA for Triple-A Memphis, started in place of Carlos Martinez, who was scratched with back soreness but is expected to make his next turn.

"It's been an up and down year for me as everybody knows," said Gonzales, who was an effective rookie on the Cardinals' NL championship series team last fall but has been slowed by injuries this season. "It's a learning experience, for sure."

Carlos Villanueva replaced Gonzales and restored order, allowing one hit in 3 1-3 innings with a season-high six strikeouts.

"He's done that all season," Matheny said. "He helps Marco get out of that inning and then he sails."

TRAINER'S ROOM

Nationals: Stephen Strasburg, limited to four innings by upper back tightness in his last start, played catch without problems. If he feels well, he'll be scheduled for a bullpen session that would keep him on track to go Friday against Atlanta.

Cardinals: Matt Holliday took batting practice at Busch Stadium for the first time since straining his right quadriceps muscle and lined several homers. Lefty Tim Cooney will be shut down after three weeks of inactivity following an appendectomy.

UP NEXT

Max Scherzer (11-11, 2.88) tries to shake off a forgettable August in which he was 0-3 with a 6.43 ERA and surrendered seven homers in five starts. Michael Wacha seeks his 16th victory and was 3-0 with a 1.13 ERA in August.

HOT ROOKIE

Stephen Piscotty had two hits and is 16 for 38 (.421) during a nine-game hitting streak. He has 12 multi-hit games in 38 games.