The Bayern coach saw his side run riot at the Stadio Olimpico last month in the sides' UEFA Champions League Group E encounter, as the German champions surged into a 5-0 half-time lead.
Further goals from Franck Ribery and Xherdan Shaqiri late on ensured Bayern's biggest away win in UEFA competition and put them on the verge of the last 16.
Victory at the Allianz Arena will see Bayern through but Guardiola insists his side must approach the game in the right manner.
"It's a different game. We're focused on the massive chance we have to progress to the next round," he said on Tuesday.
"We start at 0-0. This is a new game and we must focus on our style of play to reach the next phase.
"[Roma] have their pride and will not want to lose the game again. They have a very good and youthful side who can impose their game on you if you give them too much room.
"We're playing better than I thought we would, but we're not quite at the level where I want us to be."
Bayern come into the game with plenty of confidence, having seen off rivals Borussia Dortmund 2-1 in the Bundesliga on Saturday.
Franck Ribery played a key role in inspiring Bayern's comeback from a goal down as he continued his return to full fitness following back and knee injuries with Guardiola confirming the winger may start Wednesday's game.
"He made the difference against Dortmund," the Spaniard explained.
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