DENVER -- In a season filled with improbable moments, it was fitting that the D-backs did not know immediately that they had clinched a playoff spot on Friday night.

As closer Jose Valverde pumped his fist after striking out Kaz Matsui to nail down Arizona's 4-2 win, D-backs PR director Mike McNally grabbed manager Bob Melvin in the dugout and told him that the Mets had lost to the Marlins, meaning the D-backs were in the postseason, either as National League West champs or the Wild Card.

"Are you sure?" Melvin asked McNally.

"Yes."

"Are you really sure?"

"Yes, I'm sure! We're in!"

It was only then that Melvin yelled to his players, who were heading out of the dugout as if win No. 90 were just an average win.

All of it led to a delayed on-field celebration, but by the time they reached the clubhouse, the champagne was flowing and the party, which will no doubt last long into the night, was beginning.

Still, Melvin wanted to make sure one more time, as he hugged general manager Josh Byrnes just outside the manager's office.

"We're in, right?" Melvin asked.

"We're in," Byrnes said.

Yes, Arizona is in the playoffs for the first time since 2002, when it won the NL West and was eliminated in the NL Division Series by the Cardinals. Next week will be the organization's fourth postseason appearance in its 10-year history.

With one more win or a San Diego loss, the D-backs will be NL West champions. If Arizona should drop its final two games and the Padres win their last two, then Arizona would go in as the Wild Card.

Coming into the game, the D-backs needed to win and also have either the Phillies or Mets lose to clinch a spot. The Phillies beat the Nationals, 6-0, in a score that was posted on the right-field scoreboard midway through the game. The Mets, on the other hand, trailed Florida, 7-4, heading into the bottom of the ninth inning and though the game ended prior to Arizona's, it wasn't posted as a final, hence the confusion.

"Until Mike McNally, our PR guy, came out on the field and told us what had happened, we had no clue," veteran first baseman Tony Clark said. "We knew that if we won a ballgame, then we'd have a chance. Since we couldn't control anybody else, that's what we tried to commit ourselves to."

Arizona came into the game with its ace, Brandon Webb, on the mound after the club decided to push his start back a day because of weather concerns in Pittsburgh on Thursday.

The right-hander had struggled against the Rockies this year, going 0-3 with a 6.47 ERA in five starts. Add in the fact that Colorado came into the game riding an 11-game winning streak and Arizona knew it had a tall order in front of it.

But Webb was on top of his game from the start, as he did not allow the sellout crowd to fully get into the game. The right-hander allowed just one run through the first six innings and pitched out of a couple of jams, one in the second and one in the third.

"It got pretty loud," said Webb, who raised his record to 18-10. "It was like a playoff atmosphere. A couple of times, it got supersonic out there with that sold-out crowd. I was trying to keep my emotions in check."

While Webb was setting down the Rockies, the D-backs were making Jeff Francis work hard in the early innings, and took advantage of a break in the second.

With runners at first and second, Stephen Drew hit a sharp grounder back up the middle that Francis deflected with his glove. Had the lefty not touched the ball, it looked like the Rockies would have been able to turn an inning-ending double play. Instead, Drew was able to beat it out and Augie Ojeda followed with a sacrifice fly to put Arizona up, 1-0.

In the third, with two outs and one on, first baseman Conor Jackson looked at strike one from Francis on a pitch he thought was outside the zone.

"It didn't matter," Jackson said.

That's because Jackson deposited the next pitch in the left-field bleachers for a 3-0 Arizona advantage.

"When it left the bat, it was still early in the game, so I really didn't think with a team like that, with an offense like that, two runs probably isn't going to hold up in the game," Jackson said. "Tonight, we were fortunate enough that it did."

The game was not without its anxious moments, though, as the Rockies put together a rally in the ninth against Valverde.

With one out, the big right-hander walked two straight batters. That brought a visit from pitching coach Bryan Price and Valverde settled down to fan the next two to end the game and start the celebration.

Well, the sort-of celebration.

"I just wanted to be sure," said Melvin, who certainly is the front-runner for NL Manager of the Year. "I didn't want us to look foolish."

They looked anything but on this night. Instead, they looked playoff bound.