Hader, who collected his fourth save of the season Monday, went 2⅔ innings to secure the Brewers' win over the Cincinnati Reds. He got seven swinging strikeouts and one on a bunt attempt that went foul. He also walked one batter.
Asked to describe this performance, Hader said, "Fun. A lot of fun.''
Monday's outing was the longest of the season for Hader, but he said he wasn't concerned about the extra work.
"Just attack the hitters, and whenever [manager Craig Counsell] comes up to me and says I'm out, that's my mindset," he said. "I don't limit myself on how many I go. Whenever I hear, 'You're done,' that's when I'm done."
The hard-throwing lefty has struck out 39 batters in 18 innings of work this season.
"I don't think anybody could hit him tonight,'' Reds interim manager Jim Riggleman said of Hader's outing.
Opposing batters are now 0-for-49 with 39 strikeouts against Hader with two strikes this season. Hader has struck out 62.9 percent of batters that he has faced (39 of 62), which is by far the highest strikeout percentage in MLB.
"I don't know what to say about Josh," Counsell said. "Literally, your mouth is kind of wide-open watching it. It was absolutely incredible."
Corey Knebel, who went on the disabled list with a left hamstring strain on April 6, entered the season as the Brewers' closer. He threw live batting practice Monday.
"It went fine," Counsell said. "... We're definitely making progress."
Counsell said Knebel, who tallied 39 saves and was an All-Star selection in 2017, may be able to return for the Brewers' next road trip, which begins May 10 in Colorado.
The Associated Press contributed to this report.