Black's rationale is simple: He wants Peavy pitching in the last game of the season and in an elimination game. Who better than Peavy -- a 19-game winner and Cy Young favorite -- to take the ball?
"We thought that it might come down to this, the way the season was winding down and the race in our division," Black said. "The way our rotation worked out ... we felt if this day happened, we had Jake on regular rest."
Weeks ago, Black indicated that Peavy -- who last pitched Wednesday against the Giants -- could be brought back on three days' rest in the final game of the regular season, though only if that was a must-win game for the Padres.
It wasn't, as the Padres on Friday had guaranteed themselves of at least a tiebreaker game with a victory over the Brewers. That made Black's decision to go with Brett Tomko a lot easier.
Of course, Black likely never envisioned a scenario where the Padres would lose a lead in the ninth inning of Saturday's game in falling to Milwaukee, nor did he ever think Tomko would lose all of an early 3-0 lead and not get out of the fifth inning.
But that's what precisely what happened.
The Padres tried bringing Peavy back on three days' rest last month against Arizona, but Peavy had his worst start of the season, allowing eight earned runs over four innings.
More Peavy: Five days ago, Peavy picked up his 19th victory in the Padres' 11-3 victory over the Giants at AT&T Park.
Peavy limited the Giants to two runs on five hits over seven innings with one strikeout -- a number that might be cause for concern for a pitcher who led the National League in strikeouts this season.
Peavy even said after the game that he didn't always have a great feel for his pitches, and his command wasn't as sharp as it's been during a season where he's built the credentials of a Cy Young favorite.
"He probably had his worst stuff of the year tonight," Padres catcher Josh Bard said after the game. "He's found a way to win without his best stuff. That's where you start separating yourself as an elite player in this game."
"He kept the ball down, got a lot of balls hit on the ground," Black said. "I thought that his changeup was better Wednesday than any other time of the season. That's a good sign.
"I think it shows the maturity of Jake where he utilized all his pitches and didn't just rely on stuff. That's a great sign for him."
Peavy was named the National League Pitcher of the Month on Monday. He went 4-1 with a 3.20 ERA in six starts in September.
Busy bullpen: The Padres leaned heavily on their stable of bullpen arms during a four-game series against the Brewers, as San Diego relievers combined for 16 1/3 innings in four games.
But Black was able to stay away from three of his top relievers during Sunday's 11-6 loss to the Brewers, as closer Trevor Hoffman, Joe Thatcher and Heath Bell didn't pitch.
"Cla [Meredith] has been out there quite a bit. If he pitches, it will be five days in a row. That's a little taxing," Black said. "The other guys, Bell, Thatcher, [Justin] Hampson had yesterday off. [Doug] Brocail is relatively fresh. Hoffman had the day off.
"The bullpen has been taxed, but I think the guys should be ready."
Opportunity knocks: The Padres' game on Monday against the Rockies wasn't officially a postseason game, but don't tell that to outfielder Scott Hairston.
"I guess technically, it's the regular season. But it feels like the postseason. ... It's a one-game thing. It's do or die," said Hairston, who started his eighth consecutive game in left field on Monday.
Hairston is hitting .188 since replacing Milton Bradley in the starting lineup. Brady Clark -- who is starting for an injured Mike Cameron -- is hitting .346 in that same eight-game stretch.
"It feels great, to get the at-bats every day, especially on a team like this," Hairston said. "I've got a chance to get in a groove and perform, go through the ups and downs like everyday players do."
On deck: If the Padres win, they advance as the National League Wild Card and will face the Phillies in Philadelphia in Game 1 of the National League Division Series on Wednesday at noon p.m. PT. If the Padres lose, their season is over.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.