Yet, it was slower, much slower and walked on all fours. If the T-rex were able to push it onto it's back, it's spines would shatter and it would die. The only way the Spinosaurus would win is if it could latch onto the T-rex and the T-rex doesn't thrash around. Outside of that it's pretty one sided. Another point is that T-rex teeth were meant for tearing at flesh and splitting bones, while Spinosaurus teeth were more suited to fishing. The Spinosaurus would also win if the battle took place in water, since they were partially aquatic. But I'm assuming this battle takes place on land.