The Irish champions settled quicker on a bumpy surface and Arlene Boyles had an early penalty corner shot well saved by the keeper.
The front three of Claire McMahon, Susie Beaney and Alex Spears all looked extremely sharp but had to contend with some very robust tackling from the Lille defence.
Nadine Brown had a superb run down the right and almost scored from close range but it was the thirty third minute before Pegasus turned their possession into a goal.
It was their third penalty corner and a switch went left to Jill Orbinson whose shot was neatly turned in by Julie McNight at the far post.
The half time whistle came shortly afterwards with Pegasus deservedly in the lead.
In the second half Pegasus were always the better team winning seven penalty corners without conceding any but they found it difficult to get through the French defence which certainly knew how to break down play often without much ceremony.
McMahon was in fantastic form but even her magical skills were not enough to beat some tough tackling which was not always dealt with by the umpires to the satisfaction of the travelling Pegasus support.
Pegasus play Polish side Brzezney on Friday in their second group game and coach Billy McConnoll will be hoping the girls can dominate like they did on Thursday but have more success finding the back of the net.