This secured the talented Wallace the Ulster Number 15 shirt for the next series of games including the 27–21 defeat of Edinburgh to lift the Celtic Cup, Ulster's first piece of silverware since the famous 1999 European Cup triumph, and the 33–0 thumping of Leicester Tigers at Ravenhill in January 2004, in the return leg of the Tigers' fixture though he had a torrid time playing at full-back and was relegated to the bench for the majority of the remainder of the season. Wallace had 3 more starts that season, twice at outside centre and once again at fullback, all due to injuries to other squad members. He was though successfully used as an impact substitute off the bench scoring a number of tries from here.
The 2004/05 season started well for Wallace, playing from out-half he hit the winning drop goal in the 17–16 defeat of Edinburgh at Murrayfield but after this the Ulster team and himself both suffered a massive dip in form. After the home defeat to Leinster in September 2004 he was relegated to the bench to accommodate David Humphreys at out-half. He made a number of appearances off the bench in this period but having come on for David Humphreys in the away Heineken Cup defeat to Gloucester he damaged knee ligaments that would see the him ruled out until the new year.
