Johnson became the Football League's youngest manager at just 31, when he took over from Paul Dicov, and the Latics were on top form at Boundary Park.
The 3-0 win sees them move above Scunthorpe and out of the relegation places.
"I'm so proud of the lads. I really feel it for them. I'm not that bothered about myself, although it's a weight off the shoulders to get that first win straight away, but I've been really backed", Johnson said.
Iron fans will have one eye on Oldham at the weekend as they play early strugglers Shrewsbury, who have recently pulled away from the bottom four themselves.
"Of course you're a bit nervous going into your first job and doing your first team talks, because that's the sort of thing I haven't done".
"I'm just trying bring out the best in each player", he added.
Oldham have one game in hand over Scunthorpe and Bury and two games over Hartlepool and Portsmouth, who are in danger of being cut adrift at the bottom.