ST. LOUIS -- Jake Westbrook threw a pain-free bullpen session on Saturday morning. It was the last checkpoint the right-hander needed to pass before being cleared for a Minor League rehab assignment.
Westbrook is scheduled to begin that assignment on Tuesday with a start for Double-A Springfield. He's expected to throw about 60 pitches in what will be his first game appearnace since May 8. Westbrook is hopeful that it'll be the first of only two necessary starts in the Minors.
"It will be interesting to see the up and down," Westbrook said, referring to the starting and stopping starters go through each inning. "I'm excited about how I feel."
Due to Friday's rainout, the Cardinals will need someone to start Wednesday's game in place of previously-scheduled starter Shelby Miller. Don't plan on it being Westbrook. The club intends to have Westbrook build himself up to where he'd be ready to throw 100 pitches upon his return to the rotation. He will need at least two starts to get to that point.
The decision to have Westbrook make his first rehab start with Springfield instead of at Triple-A Memphis was merely the result of convenience. Springfield is at home next Tuesday, while Memphis is on the road.
Matheny weighs rotation options for Wednesday
ST. LOUIS -- With Shelby Miller's start being bumped to the first game of Saturday's doubleheader, the Cardinals rotation is now out of sync. Miller was originally scheduled to pitch again on Wednesday against the D-backs.
Manager Mike Matheny said the club will address the start over the coming days.
"We'll check out Wednesday when we get there," Matheny said. "But we have some options, depending on what happens between now and then."
If Matheny were to look to his bullpen for a starter, the most likely candidate is Joe Kelly, whom he said would have started Friday night had the game started with severe weather still threatening to cause in-game delays. Kelly has allowed 14 earned runs on 29 hits and seven walks while striking out 19 over 18 2/3 innings this season.
Jake Westbrook is beginning a rehab assignment at Double-A Springfield on Tuesday, but Matheny said he doesn't think the injured right-hander will be ready to go by Wednesday. Minor League options have been depleted in recent weeks, as the Cardinals have had to turn there with the numerous injuries to their pitching staff.
Matheny didn't rule out using a player on short rest, but said he wasn't in favor of that option. If one of Saturday's starters sees limited work, he said they could go again on just three days' rest. Game 2 starter Adam Wainwright has never started a game on fewer than four days of rest.
"Never rule anything out until we just kind of watch how things go," Matheny said. "We just don't get too far ahead."
Butler tosses scoreless frame in Major League debut
ST. LOUIS -- Keith Butler began Friday in Midland, Texas, ended the day in St. Louis and found himself jogging to the mound at Busch Stadium by Saturday afternoon. A day after being in uniform for his first big league game, the 24-year-old Butler kicked off his Major League career with a scoreless appearance in the Cardinals' 8-0 win over the Giants.
Butler said he began to think Saturday would present an opportunity for him to pitch once the Cardinals jumped on Giants starter Matt Cain in the third inning. He later watched Victor Marte warm up, hoping the next phone call to the bullpen would include his name. It did.
"I said, 'All right, just go out and treat it the same as any other outing,'" Butler said. "It wasn't really much different running out there. But when I got to the mound, I did a turnaround to take it in a little bit. It was by far the best feeling ever."
Butler, now the fifth Cardinals pitcher to make his debut this season, allowed a leadoff walk before notching his first strikeout. The ball was thrown to the dugout to be presented to Butler after the game. After giving up a hit, Butler closed the inning to seal the Cardinals' Major League best ninth shutout of the season.
He did it in front of his parents, too, who had traveled from their home in Kentucky to be in the stands.
"When the two outs happened and everybody stood up and started cheering, I can't explain that. That was absolutely amazing," Butler said. "It's been crazy. After traveling on the plane to St. Louis, it started sinking in more and more. And once I was running out to the pitcher's mound, it really dug in right there."
• Matheny was not going to have Yadier Molina catch both games of the doubleheader on Saturday, and he eventually settled on the nightcap as the one for Molina to play. That allowed Tony Cruz to get his fourth start of the season, and second with Miller on the mound.
• The Cardinals finished May with a 20-7 record, nearly matching their best May winning percentage in franchise history. The 1971 club had a .760 winning percentage (19-6). This year's club finished with a winning percentage at .740. After opening the month with a half-game lead in the division, the Cardinals start June with a two-game advantage over the Reds and Pirates.
• Jon Jay entered Saturday hitless in his last 19 at-bats. His batting average has dropped from .276 to .250 during that stretch. With Carlos Beltran out of the lineup for the first game of Saturday's doubleheader, Jay was bumped up to the second spot in the lineup. He broke his skid, going 1-for-4 in the Cards' 8-0 Game 1 win -- delivering an RBI single in the seven-run third inning.
• Left-hander Marc Rzepczynski made his fourth straight scoreless appearance for Triple-A Memphis on Friday. Rzepczynski, who was sent to the Minors in late April, has been passed over for a promotion several times since. In 17 innings with Memphis, Rzepczynski has allowed six earned runs and walked nine.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. Chad Thornburg is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.