JOE WRIGHT kicked the crucial penalty on 64 minutes before disciplined defence helped Ionians to victory.
They had made a strong start but went behind after receiving two yellow cards.
James Ferguson broke a robust defence with a chip through w
hich was dived on by James Greene for the try.
Ferguson missed the conversion then hit the post with a penalty. The Lions did likewise before two yellow cards in two minutes enabled winger Tom Harris to kick through to score against 13 men, Jack Green converting.
Once back to full strength after the break, it was all Ionians but defences were on top.
Finally, after Ferguson and Wright both sliced penalties, Wright kicked what proved the winning goal from in front of the posts.
Hull 29
Waterloo 13Hull secured an important win to give themselves a much-needed lift out of the bottom three.
An early penalty for the visitors gave Liam McGovern a long-range kick to open the scoring. Hull responded by setting up a try for winger Chris Murphy before Matt Davies celebrated his return from injury to put Hull 10-3 ahead by half-time.
Guy Martinson, making a club record 209th appearance, celebrated with a try just after the restart following a surging run from the outstanding Laurence Pearce.
Pearce and Robin Kitching claimed similar tries which earned the bonus point as good passing exposed the defence on the right.
Mark Rylance scored a consolation try with 10 minutes remaining but Hull had enough possession to register victory.
Preston Grasshoppers 17
Huddersfield 11Huddersfield's losing run was extended to seven league games but they performed better than in recent weeks.
This was a scrappy match in difficult conditions and one in which a home forward was sent off for butting and Huddersfield received three of the four yellow cards.
Chris Johnson's penalties either side of a Preston try saw Huddersfield take a 6-5 lead which they extended with an excellent try, Matt Clark making a break and keeping the ball alive in the tackle to put full-back Tom Owen over.
The 11-5 advantage remained until half-time but Preston muscled their way over for a try.
Huddersfield conceded a converted try when they were down to 13 men, although they had a late opportunity which was lost following a disputed turnover near the line.