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5/17/2013 7:57 P.M. ET

Top prospect Wacha continues to roll at Triple-A

ST. LOUIS -- Highly touted pitching prospect Michael Wacha lowered his season ERA to 1.89 ERA with the most dominant start of his professional career on Thursday.

Wacha, the Cardinals' top pick in the 2012 First-Year Player Draft, retired the first 13 Tacoma batters he faced en route to finishing seven innings for the third time this season. Rich Poythress' home run cost Wacha the shutout, but it was one of only two hits the right-hander allowed. Wacha walked one and struck out eight in the outing.

"It sounds like he's doing everything he needs to do right now," manager Mike Matheny said of Wacha, the organization's fourth-best prospect according to MLB.com.

Wacha remains undefeated in Triple-A, though the Memphis bullpen cost him a fifth win on Thursday. Since being knocked around in his first Triple-A start, Wacha has held opponents to eight earned runs and a .159 batting average over 43 2/3 innings.

Scar tissue delays Westbrook's recovery

ST. LOUIS -- Initially hopeful that elbow discomfort would sideline him for only two starts, Jake Westbrook is now bracing for a slightly longer-than-expected stay on the disabled list. Additional tests on Westbrook's right elbow this week revealed a build up of scar tissue, which required a second cortisone shot in the elbow.

The shot, which Westbrook had on Thursday, precludes him from throwing for two days. That meant Westbrook could not resume his throwing program on Friday as had been originally scheduled. Even if he can begin playing catch again on Sunday, the setback is likely enough to cost Westbrook a third start.

"The fact that I haven't thrown yet, it would probably be tough to gather enough arm strength up to make that next start," said Westbrook, who will be eligible to come off the disabled list on May 24. "But you never know."

John Gast started in Westbrook's place on Tuesday and will do so again on Sunday. Westbrook's turn in the rotation would come up next on May 25 -- or May 28, if the Cardinals chose to push it back by taking advantage of a day off next Thursday.

Westbrook was placed on the DL with what the club had described as elbow inflammation. He had also been bothered by biceps tendinitis. News that scar tissue was affecting muscle flexibility in his elbow came after Westbrook underwent an MRI this week.

He said he suspected there was another issue given that the first cortisone shot alleviated discomfort only temporarily. The MRI did show that there was no structural damage, which has Westbrook optimistic that the overall issue should not keep him sidelined extensively. The evidence of no structural damage was welcome news for a pitcher who has already undergone elbow surgery twice in his career.

"I think it's just a combination of the amount that I've thrown over my career and the surgeries that I've had," Westbrook said. "It's definitely not a brand new elbow. It has lots of things going on in there. Everything looked great other than the scar tissue. If anything, I've got that going for me, which is nice."

Cards not concerned with high double-play totals

ST. LOUIS -- After hitting into another two double plays on Thursday, the Cardinals' twin-killing total is on the rise again after dipping last season.

The club has already grounded into 38 double plays, putting the Cardinals on pace to hit into 154 this season. That would be only two fewer than the Major League high last season, set by the Tigers.

The Cardinals' susceptibility to ground in double plays was scrutinized at length in 2011, when they hit into 169 of them. That number dropped to 135 last season, though still good for eighth-most in the Majors. The team's current total of 38 is third-worst in the National League. Ten of those double plays have come off the bat of Matt Holliday.

The overall number, though, is not drawing much attention in the Cardinals' clubhouse.

"I don't think we've hit into as many double plays this year as we did in the past," Allen Craig said. "Sometimes you hit it hard and it goes right at them."

Of course, with one of the league's best on-base percentages (.328), the Cardinals also find themselves with more opportunities to ground into double plays than most other NL clubs. The Cardinals' overall proficiency with runners in scoring position -- a team .327 average heading into Friday's game -- has also masked many of the other rallies that were thwarted by double plays.

"We just want guys taking good hard at-bats," manager Mike Matheny said. "And if they hit it hard at somebody, you have to tip your hat. Especially when you have first and second, they're looking to drive the ball hard up the middle. You get it a little too far to the left or the right, it's right at somebody. I think that's been the case more than anything else."

Worth noting

• After making five scoreless appearances to open his Triple-A stint, reliever Mitchell Boggs was knocked around for three runs on two hits and three walks while only notching one out on Thursday. He threw just 12 of his 27 pitches for strikes.

• Triple-A infielders Kolten Wong and Ryan Jackson are both riding nine-game hitting streaks for Memphis. Wong is batting .405 with a .444 on-base percentage during that stretch. Jackson has a .474 average and .524 on-base percentage over his last nine games.

• The Cardinals announced on Friday that registration is open for the Ted Savage RBI Golf Classic, which will be held at the Forest Park Golf Course in St. Louis on June 11. The tournament, which is hosted by Cardinals Care, will include several former Cardinal players, including Whitey Herzog, Lou Brock and Andy Benes. Money raised through the event will go to the Reviving Baseball in Inner Cities Program to help kids in the St. Louis community.

For more information on the event, go to cardinals.com/rbigolf.

Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.