I would have said Bellew is boxing smart rather than looking like he's run out of steam
Think it was a bit of both.
He threw a lot of punches after Haye was injured for a couple of rounds and think he definitely felt the pace. In saying that he knew he was ahead and I think he chose to slow the pace to give himself a breather as much as anything.
I fell in love with football as I was later to fall in love with women,. Suddenly, uncritically giving no thought to the pain it could bring. - Nick Hornby