Quins secured third place in the table with their 22-19 victory over Northampton Saints in front of a sell-out 14,800 crowd at the Stoop.
They have already beaten the Tigers 22-9 at Welford Road and 25-22 at the Stoop this season, but director of rugby O'Shea said: "That's kind of irrelevant. The next game is always the big game so we need to turn up with the mindset we had, the intensity and the intent we had, but we have to do it for 80 minutes."
He went on: "If you go to Welford Road and you don't do it for 80, it's not good enough. We are ready for the incredibly exciting test next week. If we can take our chances we'll be right in it."
O'Shea admitted the result was closer than it should have been after Northampton hit back from 22-5 down to cut the deficit to three points.
Wing Tom Williams, hooker Rob Buchanan and centre Tom Casson scored tries for Quins, with fly-half Nick Evans landing two conversions and a penalty.
Saints replied with tries from left wing Jamie Elliott, hooker Dylan Hartley and lock Christian Day, on his 100th appearance for the club, but their fightback fell just short.
England scrum-half Danny Care, also overlooked by the Lions, responded with a man-of-the-match display and O'Shea added: "Danny knows how to bounce back."
Northampton director of rugby Jim Mallinder said: "It's an unknown for us being away to Sarries in terms of the new pitch there.
"But we're not going to go there worried about them. We know they are a quality side, very difficult to beat, but we also know that, on our day, we've got a real good team."
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