Simpson gave Latics a 1-0 lead courtesy of a spectacular long-range effort when the two sides met in last season's third round at Anfield, but the Reds were in front by half-time and a pair of late goals added considerable gloss to a 5-1 scoreline.
A brace from Simpson inspired Paul Dickov's men to the shock comeback win over Nottingham Forest that set up Sunday's Boundary Park clash one step further along the road to Wembley, and the versatile former Coventry and Huddersfield forward feels Oldham's status as the home side may change the complexion of the contest.
He said: "Last season it was kind of seen as a day out at Anfield, whereas this season we've got them at home and we know how we have done against them in the past.
"It's kind of like 'can we beat them?' rather than 'let's have a day out'. It's a different mentality, I guess."
Simpson admits he regularly watches his moment of magic in front of the Kop but ultimately feels Oldham were short-changed for their efforts on Merseyside.
"It definitely was an unfair reflection," he said. "We went in at half-time 2-1 down, looking at each other saying 'how are we 2-1 down?'.
"We played some really good stuff and if we'd gone in 1-0 it would have been deserved. They got a lucky deflection for their equaliser just after I scored and then they got given a penalty which was a little dubious.
"In the second half we came out in the first 10 or 20 minutes and had a couple of opportunities. It was the last 20 minutes of the game where they scored three goals in quick succession. It didn't reflect the game."
Liverpool won the previous encounter under Kenny Dalglish's management and Brendan Rodgers' meticulous passing approach is likely to present different problems this time around.
The Premier League outfit have won eight of their past 11 games in all competitions, a run very much at odds with Oldham's dismal recent slump that has returned a solitary point from eight npower League One matches.
Nevertheless, Simpson takes encouragement from the manner of non-league Mansfield's 2-1 defeat to Liverpool in the previous round, along with Latics' superb City Ground triumph.
"All of us watched the Mansfield-Liverpool game and it just showed that Mansfield gave them a right good go and stopped them playing at times," he said.
"When Liverpool did have good possession they let them have it but as soon as a pass went astray they were right on it and pressing in their faces.
"Forest were similar, the way they shaped up. They had a deep-lying midfielder who always got on the ball and were quite methodical in their passing.
"In the first half of that game we let that dictate us but second half we got in their faces and stopped them doing that.
"We can take heart from that and we can maybe do the same against Liverpool."