"For me, it's not a tough call at all," Melvin said.
Webb led the National League with a career-high 236 1/3 innings this year, and in 165 career big league starts he had never pitched without having at least four days between starts.
Rookie Micah Owings, who has not pitched since Sept. 27, got the ball instead. Owings tossed 15 1/3 scoreless innings in his final two regular-season starts.
"My thinking from the very start is that this guy has pitched a lot of innings, and he's never done this before, and the track record behind it is not very successful and we have other guys we feel confident in," Melvin said. "Now, would I rather have Brandon Webb out there every night? Absolutely. But just based on all those things, I just didn't feel like it was the right thing to do to a guy that's never done that before."
Had Webb started Game 4, he would have been able to pitch Game 7, had it been necessary, on regular rest, but Melvin cited the fact that a pitcher like Orel Hershiser, who both started and relieved during the 1988 postseason, eventually needed arm surgery.
"It scares me a little bit," Melvin said.
For his part, Webb said he understood the decision, and he did not approach Melvin and ask to start. Webb was 1-3 with a 5.77 ERA in six regular-season starts against Colorado and was the loser in Game 1.
"There's just factors that have gone into it that really just make it kind of unnecessary," Webb said. "I've never done it before. With the innings I've accumulated in the last couple of years, I've been leading the league in innings, that's another factor. You know, if I was 5-0 against these guys in the regular season, I probably would be a little bit more open to going out there and doing it today.
"And also, we gotta win four more games anyway. Micah is going to have to win a game, every one of our starting pitchers is going to have to win a game. I can't go out there and pitch every game."
Mixing it up: Augie Ojeda started the first six games of the postseason for the D-backs, but with the offense needing a spark, Melvin turned to Jeff Cirillo for Game 4.
"Augie's done a phenomenal job for us," Melvin said of Ojeda, who filled in admirably after starting second baseman Orlando Hudson suffered a season-ending thumb injury in early September. "But just because of our offensive woes, I'm just looking to get another look in there and a guy that's had success against left-handed pitching."
Entering the postseason, Cirillo had played the most games (1,617) of any active player who never had his team make the playoffs.
"Obviously it's the biggest game of the year," Cirillo said. "I'm not nervous, I'm excited."
Stuck in the mud: A big part of the D-backs offense during the regular season involved the stolen base, and Melvin was asked if he had considered stealing during Game 3, which was played in a steady rain.
"Guys had green lights, they just weren't comfortable at times going," Melvin said, referring to the muddy conditions on the basepaths.
Impressed: Dustin Nippert, who was a starter throughout his Minor League career, pitched out of the bullpen during his time in the big leagues this year, and has tossed 2 1/3 scoreless innings in the NLCS.
"He's been great for us," Melvin said. "Whether or not this is his niche, he's done very well in this type of role. I think there is probably some debate within the organization whether or not he's going to be a starter or a reliever, but he's given himself some options."
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.