"Working behind on every single batter gets old and gets frustrating," Isringhausen said.
During the month of May, though, the only ones frustrated were Cardinals opponents. Izzy walked eight hitters in 11 2/3 innings, but kept his control problems at bay.
"He's been in a lot of stressful games," Cardinals manager Tony La Russa said.
Izzy collected a perfect 10 saves in 10 opportunities and posted a 0.77 ERA in 11 games. His month earned him the Major League Baseball Delivery Man of the Month Award sponsored by DHL.
La Russa said Izzy's control problems won't be a factor -- if he continues to save games.
And after a rough patch at the beginning of the season, Isringhausen, second on the all-time Cardinals save list behind Lee Smith, has been lights out.
Entering Tuesday's action, the veteran's 18 saves were tied for the National League lead with the Phillies' Tom Gordon.
"He has proven that, when he is himself, he is a quality closer," La Russa said. "He has a good save total and his percentage is still high."
The right-hander's ninth-inning work has kept the Cardinals firmly in the driver's seat in the National League Central and helped maintain a 3.18 bullpen ERA, the lowest in the Major Leagues.
Isrighausen also has preserved many victories for the starting pitchers, a quintet that has accumulated 27 wins, the most in the NL. One key victory came on May 24 against the Giants.
He walked two hitters, before retiring the side and closing out a win for Jason Marquis.
"He did what he usually does," La Russa said of Izzy. "He didn't panic, he [collected] himself and he got the outs."
Conor Nicholl is an associate reporter for MLB.com This story was not subject to the approval of Major League Baseball or its clubs.