The League One Latics were hard to beat at Anfield as the Reds finally overcame them with second-half goals from Iago Aspas and an own-goal from James Tarkowski.
Johnson was thrilled with the manner in which his Oldham side went about it, especially after dominating small portions of the contest.
"We worked our socks off first half, we broke well and got ourselves into areas where we had shots," he said.
"We had corners, free-kicks...so we certainly weren't just parking the bus. I thought our boys showed energy, particularly when we went 1-0 down. For a 20-minute period you may not have known who was the Premier League side.
"We passed and moved and had a good couple of chances.
"They can go home, look at themselves in the mirror and say that they've competed on a massive stage in front of world-class players and world-class fans. They can enjoy the fact that they've produced their best game."
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