Harlequins were frustrated in their efforts to repeat the accomplishment of last season when they had teams in the finals of both men's and ladies' competitions.
It was no consolation that they provided two of the game's high points.
One was the marvellous strike that put them into a lead after just 14 minutes. Emer Dillon, an inter-county camogie player with Cork, showed flawless technique as she took a ball wide of a tackle before flashing home a reverse-stick shot of great power and accuracy.
The other was the magnificent goalkeeping exhibition of Orla McCarthy. She defied a talented Pegasus strike force with a stunning save from a penalty stroke and then with a remarkable double save in the middle of an intensive spell of pressure.
Pegasus survived a nervous opening half to hit their stride in the second. An equalising goal within a minute of the re-start from Nadine Graham was all the encouragement they needed to dominate the game and add further goals through Sarah Wilkinson and Claire McMahon.
A key influence on the trend was the outstanding play in central midfield of Humphreys, a brother of rugby star David, and the elusive running of McMahon.
Harlequins coach Ivan Bateman admitted: "No, we didn't do ourselves justice. We started reasonably well and we were lucky to get a goal from the only strike we had at goal. It looked very promising going into the second half but they stepped up a gear and put us under a lot of pressure.
"They certainly worked hard. The first goal for them came early in the second half and that led to them getting a lot of confidence.
"We needed something to get back into the game which never really came at any stage apart from Orla's stroke save. I thought it might turn things around but unfortunately it didn't.
"Orla kept us in the game, she made one great stroke save and then made several other excellent saves as well."
: S. Moffett; N. Graham, S. Wilkinson, A. Boyles, F. Ferguson; P. Magill, K. Humphreys, K. McCallum; C. Redpath, S. Martin, C. McMahon.
: O. McCarthy; J. Hyland, J. Dillon, N. Kearney, J. Barry; M. Ahern, R. Kohler, K. Bateman; J. Chapple, E. Dillon, C. O'Callaghan. Subs used: A. O'Farrell, S. Canning.
: C. Metchette, C. Kelly.