A Ross Stewart penalty and a clever Elliot Embleton finish established a 2-0 lead at half time, before an own goal secured a third in the second half.
Doncaster’s squad had been heavily hit by injury and a COVID-19 outbreak in the build up, and Johnson was pleased to see his side capitalise with a clinical display.
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“It was really professional from us,” Johnson said.
“We knew it was a bit of sticky wicket for Doncaster in terms of the players they had out, though of course we do as well.
“But I remember being at Oldham and it's tough when you lose three or four players, especially against a club like Sunderland.
“We had to be professional, find control.
“The early goal helped and then I felt we forced it a bit too much, we let them off the hook a bit by trying that goal ball too often, too early. The second goal came at a really good time, it was getting a bit frustrating.
“From there the control we had was really good.”
A positive day in the promotion push was overshadowed by the news that Nathan Broadhead could be ruled out for the rest of the season, with a replacement in the January window now crucial.
“It's a disaster, we're going to need help in January,” Johnson said.
“We've got ourselves in a position where we're in the coattails of the leader, with WIgan obviously having games in hand.
“There's big expectations here and we're going to need to produce. I still think we've got another gear in us, I think we can hit top gear by adding quality [in January], getting players back, and keep hammering down on the philosophy.
“When we played simply today, which is the hardest thing to do, we looked a really good side.”