The manner of their Aviva Stadium loss to Clermont Auvergne, coupled with last Friday's derby defeat at Ulster, leaves injury-hit Leinster needing a festive pick-me-up at home to Connacht in round 12 of the RaboDirect PRO12.
"From our perspective we have to try and build some momentum coming into a busy next few weeks which will go a long way to defining the rest of the season," admitted Cullen.
"We need some big results and we need to try and get some more rhythm to our play. Against Clermont in the Aviva, we gave away too many kickable penalties and (Morgan) Parra kicked seven out of eight of them.
"Then against Ulster Paddy Jackson missed a few fairly kickable shots at goal, but Ruan Pienaar stepped up and kicked well.
"And this weekend Dan Parks will punish any penalties we give away because he has such a high kicking percentage and has proven himself time and again over the years.
"So, we need to be more careful about giving quality sides easy opportunities to keep the scoreboard ticking over. These kinds of games are won and lost over the finest of margins."
There were no major injury concerns for the Leinster management following that 27-19 loss at Ravenhill. Second row Cullen required five stitches to a cut above his eye, but he has taken a full part in training this week.
Luke Fitzgerald continues to make positive strides in his recuperation and the Ireland full-back/winger is reportedly training well. If he does not make Saturday's interprovincial clash, it is hoped that he will be in contention for the trip to Edinburgh next time out.
Neither Cullen or Fitzgerald were on the Sportsground pitch in late September when Leinster leaked five tries on their way to a 34-6 beating at the hands of Connacht.
Reflecting on what he saw that night, Cullen insisted: "We learned a few harsh lessons over in the Sportsground last time out against Connacht. I acted as water boy that day and it was tough watching from the sidelines. They brought greater physicality to the game and they dominated us in that regard in Galway."
Exacting revenge on the westerners at the RDS would go some way towards restoring Leinster's confidence as they look to inject some fresh energy into their challenge for a PRO12 play-off spot.
The Ospreys' festive derby demolition of the Scarlets - 32-3 at the Liberty Stadium - has pushed Joe Schmidt's men down to sixth in the league table and they will be eager to respond, as the Ospreys have a refixed game against the Dragons to come on New Year's Eve.
"We have to get a few more points on the board. When we get a few more bodies on deck that will boost competition for places because we've been disrupted through the first half of the season and we have lacked a bit of fluency thus far," added Cullen.
"Ulster are racing clear at the top of the league and they're going to be very hard to rein in, so we need to dig deep to get back into the top four.
"Then we travel to Edinburgh next week in the PRO12 before facing Scarlets at home in Europe and then travel to Exeter Chiefs where they have a great record at home.
"By the end of January we'll know our fate and we have a bit of ground to catch up on. And, for us, that process starts this weekend."
Tickets for the Leinster v Connacht duel at the RDS are on sale online here, and you can also purchase them from the Leinster Rugby Store (Donnybrook), Spar (Donnybrook) and Ticketmaster outlets nationwide.