Piccolomini canned a 3-pointer with 1:15 remaining in the second quarter to give Goretti a 26-16 halftime advantage.
The Gaels (15-11) opened the second half with a 10-4 run to increase their advantage to 36-20. Piccolomini scored six points in the spurt.
But St. James didn't fold.
The Saints (5-12) outscored Goretti 8-1 to close the quarter and trailed 37-28 as the final quarter began.
But Goretti put the game away with a 13-3 run to open the fourth quarter. Sophomore Brianne McManus scored all nine of her points during that stretch.
"It was a tough game," St. James coach Ted Camp said. "They were a lot deeper than we were and they move the ball better than us. They got too many second shots and we turned the ball over too much. Despite the loss, our team still gave a good effort right down to the last minute. We may not have a lot of skill, but we make up for it in grit and determination."
Megan Brown scored the final six points of the game for St. James. She finished with 16 points and seven rebounds. Carolyn Burton added 13 points and eight rebounds. Erin Call had 12 rebounds and three assists, while Tammy Hall added six rebounds, five assists and three steals.
Freshman Kristy Divelbliss added 11 points and 13 rebounds for the Gaels.
"We are very proud of the way that the girls came together and stayed together as a team," Carter added. "We ended the season on a very positive note by winning four out of our last five games. The girls worked pretty hard all year long. It was an excellent group."