Although many of Ireland's substitutes have impressed when they have taken to the pitch in those games. O'Sullivan is confident that his chosen team can do the job against Scotland this Friday in Dublin.
"The team remains the same against Scotland on the back of two good performances and we are looking for further improvement against this weekend," said the Corkman.
"Undoubtedly competition for places is high and the decision to keep the team the same was not an easy one as several players, when introduced in both our previous games, have performed really well and are keeping the pressure on the starting fifteen."
Ireland have performed well this season with a fine 19-0 win over Italy followed by a brave showing in Paris and having beaten Scotland for the first time in the Six Nations last year, the girls in green will be confident of a second victory of the season in Dublin.
However, the Scots will not travel without motivation as they are looking for their first win after losses to Wales and France, and O'Sullivan is expecting 'a very tough game' on Friday.
"Scotland have a strong forward unit. We are continuing to improve and for us as a team it is important to win our home games but we know we have to remain focused and to be at our best to achieve this," he added.
While Scotland are always strong up front, Ireland's forwards have been in fine form this season with the likes of second row Geri Healy impressing with two tries in two games and Ulster hooker Jess Limbert settling in well in the number two jersey.
IRELAND WOMEN'S TEAM & REPLACEMENTS (v Scotland, RBS Women's 6 Nations, Templeville Road, St. Mary's College RFC, Friday, February 22, kick-off 6pm):
Sarahjane Belton (capt); Lynne Cantwell, Patrique Kelly, Shannon Houston, Grace Davitt; Joanne O'Sullivan, Tania Rosser; Fiona Coghlan, Jess Limbert, Marie Barrett, Caroline Mahon, Germaine Healy, Eimear O'Sullivan, Sinead Ryan, Orla Brennan.
Replacements: Gillian Bourke, Yvonne Nolan, Kate O'Loughlin, Louise Austin, Louise Beamish, Niamh Briggs, Amy Davis.