Thomas was traded from the Phoenix Suns late in the 2014/15 season, and he would average 19 Points per Game for Boston the rest of that year.  Thomas was anointed as the starting Point Guard the year after and he would become the lowest ever draft pick (60^th) since the draft was reduced to two rounds to make an All-Star Game.  He would have a 22.2 PPG with a 21.5 PER.  That was good, but Thomas would follow that up with arguably the best season by a Celtic in the 2010s.  Not only would Thomas make his second All-Star Game, but he was named a Second Team All-NBA Selection and averaged 28.9 Points per Game (third overall) and had a PER of 26.5.   The season would however become bittersweet for I.T. as before the playoffs started his younger sister died, but he carried Boston on his back in the post-season, defeating Chicago in the First Round, and having a 53 Point Game 2 over Washington in a series win in the Second Round.  Thomas played two games in Conference Finals against Cleveland, but hip issues kept from playing any more.  After the season, he was traded to that same Cavaliers team, but his hip injury was far more severe than initially thought, and he was never close to being the same.

Overall, in Thomas 179 Games in Boston, he averaged 24.7 Points and 6.0 Assists per Game with a PER of 23.8.  Those numbers can't be ignored.