"Everybody is focused on the Wacha 'clock,'" general manager John Mozeliak told the St. Louis Post-Dispatch, referring to the nickname for big-league service time. "The clock is something that is well-documented and it’s something that we think about."

Mozeliak warned of the dangers of rushing Wacha and having to deal with Stephen Strasburg-esque issues worrying about overstressing a developing arm. Wacha, who is 4-0 with a 1.89 ERA in eight starts for Memphis, has just 68 2/3 pro innings under his belt. For perspective on how the Cardinals have handled prospects in the past who they viewed as ace material, rookie Shelby Miller tossed 383 2/3 innings in the minors before joining the Cardinals' rotation and Adam Wainwright had 793 innings in the minors (the latter split between the Cardinals and Braves organizations).

Wacha was passed over for lefty Tyler Lyons, who will make a start with the major-league club Wednesday. Although fans are wondering why Wacha wasn't promoted, general manager John Mozeliak said the team needs to be careful with the young starter. 

"We also want to make sure that we don’t put him into a situation where all of a sudden we are truly having to worry about his innings and his pitch count to the degree (of) young pitchers coming up in the past," Mozeliak said. Mozeliak also said the service time clock was playing a role in the team's decision.

The 21-year-old Wacha has a 1.89 ERA in 47 2/3 Triple-A innings. 

He didn't allow more than two earned runs in any of his first five starts. The only disappointing numbers for Wacha in April were he had nearly as many walks (11) as strikeouts (15) and he allowed three home runs. Wacha entered the season as the Cardinals' fourth-ranked prospect by MLB.com.

Wacha pitched 24 2/3 innings without allowing an earned run, which included 11 2/3 innings in major-league spring games before being reassigned to minor-league camp. Wacha struck out 28 and allowed 10 hits this spring.