He told Sky Sports News: "I have to take a huge part in it - maybe too many changes to the system. Derby took advantage in the first 20-25 minutes, and we probably made more mistakes defensively during that period than we have all season.
"We've created enough chances to get a goal, but didn't take one, and if we had maybe we'd have had a different outcome.
"We missed big players tonight and I think that showed, particularly defensively. But all credit to Derby, they've come here and played very, very well and deserved their victory probably."
Hull surrendered top spot in the Championship to the Rams as a result of their defeat.