Ulster coach Dan McFarland insists his side need to improve for Friday's return leg against Harlequins after a last gasp 25-24 victory at Belfast's Kingspan Stadium against the English side.
The Irish Province trailed 24-22 in the closing stages after two second-half tries from Quins hooker Elia Elia had edged the visitors in front, before John Cooney delivered the match securing penalty kick two minutes from the end.
Sean Reidy, Stuart McCloskey and replacement hooker Adam McBurney crossed for the hosts, with Cooney weighing in 10 points from the boot to leave Ulster top of Pool Three with three from three.
Quins, who earned a losing bonus point, had a try from Alex Dombrandt, in addition to Elia's double, with Marcus Smith converting all three tries and adding a penalty.
"We've got Harlequins away and then we have to play Clermont away and if we play like we played here in this game over at the Stoop we haven't got a chance of winning," said McFarland.
"I genuinely believe that. We're going to have to be a whole heap better than that to be able to countenance a win (at Harlequins).
"Perhaps over the last couple of weeks we've had a lot of nice things said about us in the press and I look at those and it makes me slightly nervous as I don't see us as good as that.
"This is a team that can grind out wins but is in the process of becoming a consistently good team and that's what I want (us) to be.
"We're not consistent. I'm not complaining about that, I don't think we should be consistent at this stage.
"We're on a journey and we've a fair way to go before we become consistently good.
"So, going into next week we're going to have to reassess where we're at and make sure we do the fundamentals of the game right.
"They had some good players in there who caused us trouble and perhaps we didn't expect that."
Quins coach Paul Gustard felt his side were unfortunate.
"We gave them the fright of their lives," said Gustard.
"Twenty minutes to go and nine points up, momentum was with us and unfortunately two or three key decisions went against us and allowed them to score.
"Then it (the game) was Ulster's for the taking.
"Unfortunately we fell short but there are a lot of positives to take towards Friday night.
"We're not out of the competition yet and until we find out we're out, we'll keep fighting for everything we possibly can get."