Leo Cullen acknowledged that the next couple of weeks will define Leinster's season after a hard-earned 21-18 victory over Ulster secured a Heineken Champions Cup semi-final spot.
Ulster gave the defending champions a huge test in this all-Irish quarter-final at the Aviva Stadium, leading early on through Kieran Treadwell's try with Luke Marshall's 63rd-minute touchdown bringing the visitors level at 18-all.
However, Ross Byrne completed his 16-point haul for Leinster with a decisive penalty, nine minutes from the end.
Leinster head coach Cullen said: "We know we're in two semi-finals now (in the Guinness PRO14 and Champions Cup), but it's about how we build the cohesion and our levels of performance so that, when it comes to the two semi-finals, we give probably a better account of ourselves than we did today.
"We're always having to chase the game from so early. Once Ulster had the lead, they were able to play that pressure game on us.
"We didn't respond particularly well to it, I didn't think. But ultimately we got the job done. It's pleasing on one hand, but frustrating on the other."
Ross Byrne and Adam Byrne crossed the whitewash in each half for Cullen's charges, who battled through to set up an Easter weekend semi-final against either Racing 92 or Toulouse.
Having highlighted their threats leading into the game, the Wicklow man was not the least bit surprised with Ulster's performance on the night.
"We talked about all the threats that they have," said Cullen. "(Stuart) McCloskey in the middle of the field gives them go-forward, good direction.
"We even talked about (Jacob) Stockdale going up the left hand side of the field or chipping the ball over the top when he gathered. It all played out, what we talked about."