PHOENIX -- To say that things weren’t going the D-backs’ way early in their 9-8 win over the Nationals on Monday would be an understatement.

Facing a team in the process of selling off some of its veteran players as it continues to rebuild, the D-backs fell behind 5-0 before they even got to bat. It was 6-0 after two innings.

Then things went from bad to worse in the third when first baseman Christian Walker, possibly the team’s most irreplaceable player given his performance at the plate and in the field, left the game with a tight left oblique.

“The first couple innings were very difficult,” D-backs manager Torey Lovullo said. “We got flattened.”

But they got back up.

The D-backs started chipping away at the Nats’ lead with single runs in the fourth and fifth inning, another in the seventh and another in the eighth.

Still, heading into the bottom of the ninth against Washington closer Kyle Finnegan, they trailed 8-4.

Alek Thomas led off the inning. and after catching a break when the fifth pitch of the at-bat was called a ball instead of strike three, he laced a triple to right-center. Geraldo Perdomo drove him home with a single and Ketel Marte followed with a homer to pull the D-backs to within one.

“I threw a lot of strikes, was ahead of everybody,” Finnegan said. “I think I just didn’t do quite a good enough job of executing the putaway pitch.”

Finnegan retired Gabriel Moreno for the first out of the inning before Lourdes Gurriel Jr. singled up the middle.

That brought up what would have been Walker’s spot in the lineup. Instead of letting Kevin Newman -- who replaced Walker at first -- hit, Lovullo sent up Corbin Carroll to pinch-hit.

Carroll has had his share of struggles after last year’s NL Rookie of the Year performance and Lovullo said before the game Carroll was not starting because he went with the lineup that he thought would help them score the most runs.

Carroll pulled the first-pitch splitter from Finnegan foul to right.

“Caught it out front,” Carroll said. “Not trying to hit a homer in that situation. We’ve got Joc [Pederson] behind me, a great hitter, so just trying to keep the line moving.”

Carroll would do more than that as he got another splitter from Finnegan and lined it over the wall in left for his first career walk-off homer.

“I thought I hit a fastball, but I guess it was a splitter,” Carroll said. “It was 91, but kind of just at the top of the zone, obviously not where he wanted it, and I was able to capitalize on the mistake.”

It was a stunning victory for the D-backs, and notable in multiple ways:

-- It was the fifth time in franchise history that they won a game after allowing five runs in the first inning.

-- The six-run deficit was the largest the D-backs had overcome in a win this season.

-- It was the third time in franchise history that they came from four runs down in the ninth to win. The last time it happened was Sept. 27, 2011 when they beat the Dodgers on a Ryan Roberts walk-off homer.

“That was a character win,” Lovullo said. “That was a team that played with heart and determination and a lot of will. You walk out and you’re facing an All-Star closer and you still don’t believe that’s the end. This team is hungry and it was awesome to watch. It was an awesome moment to watch from the dugout.”

Marte has come up big for the D-backs all year long, earning a starting berth at second base for the NL in the All-Star Game and he is certainly in the conversation when it comes to the Most Valuable Player award.

After the game he preferred to talk about Carroll.

“That's the ballplayer that Corbin is,” Marte said. “I've said it all the time, he's the best player we have here. He's one of the best players in the league.”

The D-backs last year qualified for the postseason by a single game before making a surprise run to the World Series, so they know the importance of every game. If it comes down to one game again, this will be one of the ones they remember.

“[Hitting coach] Joe Mather said it at the beginning of the last series -- we're never out of the game,” Carroll said. “And that’s truly how it's felt.”