Following a promising debut effort at Yarmouth, Dean Ivory's filly opened her account at the second time of asking at Doncaster before finding one too good in a novice event at Nottingham.
The daughter of Declaration Of War was a 10-1 shot stepped up to Listed class and Robert Winston settled her at the rear of the group that raced on the far side of the track.
Eirene was moved towards the centre to throw down her challenge inside the final two furlongs and she responded well to pressure to prevail by a length and three-quarters.
Johnny Murtagh's Irish challenger Sankari Royale was second ahead of Mrs Gallagher in third.
Winston said: "She probably bumped into a decent sort at Nottingham (Sands Of Mali) and it was very heavy that day over six furlongs. She just got outstayed on that ground and the drop back to five on soft ground has helped her today.
"She has always been very highly thought of. Today was obviously a chance to prove herself in Listed company.
"I think the long-term goal for her could be the Cheveley Park (needs to be supplemented). She will get six furlongs when it's not so soft.
"Dean is not too well as he has a stomach bug, but he will be here on Saturday The horses are in great form and the team are working hard at home.
"She is one of his best two-year-olds. She was very highly thought of early in the season and she is starting to prove that now."