Povetkin when he fought Joshua for the first 6 rounds at least looked sharp and when he fought Hughie Fury he looked terrible. Maybe Hughie’s style made him look bad or maybe that KO loss and year our took a lot out of him, or maybe he’s just an 8 round fighter at his advanced age.
Tommy Morrison comes to mind. From outboxing George Foreman (George would KO Moorer in his next fight) to losing by KO1 to Michael Bentt just four months later. I know I’m cheating a little, since Morrison had a fight in between against Tomashek and may have been affected by his illness.
Lucian Bute vs Glen Johnson To Lucian Bute vs Carl Froch Almost shut out Johnson and got promptly Cobraed next time out.
David Haye V Tony Bellew, in the second fight Haye was completely shot , was at least competitive in the 1st.