In a repeat of last term's PRO12 final, Glasgow Warriors exacted revenge on reigning champions Leinster as they won their season opening clash 22-20 at Scotstoun.
Glasgow went in at half-time with a 19-0 lead after tries from Peter Horne, Jonny Gray and Josh Strauss before penalties from Ian Madigan and Jimmy Gopperth got Leinster back into the game.
Jack McGrath and Tom Denton gave the visitors the lead although Glasgow were to have the final say as Stuart Hogg converted a penalty with the last kick to win the match.
Cullen was looking on from his new role as forwards coach, having retired at the end of last season, and he believes Leinster will be back closer to full strength for the visit of the Scarlets.
"We gave away two pretty cheap tries: one where the ball pops out of the scrum, another where we ripped the ball free in a tackle and Josh Strauss runs 40 metres unopposed, under the sticks," he said.
"That's 12 pretty cheap points. I thought the guys battled back pretty well from 19-0 down and the second half was a bit better.
"We'll have a few (international players) back, hopefully. That national management cycle comes to an end pretty much after this week. Generally most guys are back available for selection."
Follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up for our newsletter for regular updates on the GUINNESS PRO12
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland