Hamm made his directorial debut on the upcoming Mad Men episode 'Tea Leaves'.
Slattery – who has directed several Mad Men instalments himself – disclosed that he couldn't bring himself to prank Hamm as he originally planned.
"We tried to punk him a little bit. But there's also 50 other people standing around, and everyone knows how little time there is to shoot everything," the actor told HitFix. "I think Vinny [Kartheiser] started doing the scene and mouthing the lines with no volume, and Hamm came in and said, 'What the hell are you doing?' We had good intentions of punking him, and I chickened out."
Slattery continued: "[Hamm's] an authoritative guy. He stepped right into that without skipping a beat, and he knows how to be brief and to the point, and knows that, 'OK, we have that one, now let's try one like this, one like that, and then we're done'. It was a pretty seamless transition."
The star also directed season five's fifth episode 'Signal 30' and said he was much more "confident" this time around.
"I knew what to expect time-wise a little better. It's never easy. You think you've got it wired, and you're presented with a whole new series of challenges: location, casting, etc," Slattery explained.
The actor added: "This one, I lucked out with an amazing script, and I prepared a little earlier all the stuff I had to do on camera. I knew better to get that out of the way, so that I didn't have to worry about my performance in a moment-to-moment sense as much.
"You have these people, these actors: Vincent and Elisabeth [Moss] and Jared [Harris]and Jon, of course, and Christina [Hendricks]. You don't have to do too much. Turn the camera on and get out of the way. And then it's just a series of adjustments; try one like this, like that, and give you some options. I think it turned out very well!"
Slattery recently defended co-star January Jones against accusations made by one of the show's former child actors that she is unapproachable.
Mad Men airs on AMC in the US and Sky Atlantic in the UK.
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Watch a trailer for the fifth season of Mad Men below: