Cheika's men were beaten 27-13 at The Sportsground last night as the league's bottom-placed side overcame the runaway league leaders.
Leinster had gone into the re-arranged fixture in Galway with more than twice as many points as Connacht but they were well beaten by their Irish rivals.
"Connacht have shown pretty convincingly all season that they are a good side, even in the game up in Dublin when we were lucky to win," said Cheika, who had seen Leinster triumph 17-14 in the reverse fixture thanks to a last-gasp drop goal from Jonathan Sexton.
"I don't think that they're a bottom of the league team and we know that they have a lot of quality because we have coached a few of them ourselves."
Victory has seen Connacht climb off the bottom of the table - with the Scarlets now propping up the pile - while Leinster will have to wait at least two more days for a chance to secure a home semi-final when they travel to Glasgow on Friday.
And while Cheika was quick to praise the performance of Wednesday night's opponents, he didn't shy away from criticising the overall efforts of his own players.
"We lacked an edge in defence," added Cheika, after watching his team concede more than 20 points for just the second time this season.
"We had a lot of possession but we didn't use it properly, but in the second half we attacked the line better.
"We worked hard, but it's another game that we have lost here because we lacked the correct attitude.
"Brian (O'Driscoll) finished the game and he's fine, but Girvan (Dempsey) suffered a neck injury and we just have to manage our resources now with a game coming up against Glasgow on Friday."
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