Sillinger's stint with the Flyers began promising, scoring 22 points in the 27 games to close the season following his trade, but after managing just three assists in the first 25 games in 1998–99, he was dealt away to the Tampa Bay Lightning midway through the campaign along with Chris Gratton, in exchange for Mikael Renberg and Daymond Langkow on December 12, 1998. Sillinger, however, continued to struggle and tallied just 10 points with his new team for the remainder of the campaign for a combined 13 points between the Flyers and Lightning, a career-low.