Leonid Slutsky said former Sunderland midfielder David Meyler 'changed the game' after his half-time introduction at the KCOM Stadium.
An 82nd minute effort from the Irish international was deflected past Robbin Ruiter as the Tigers claimed a point.
Sunderland had been the better side in the first half but Slutsky's change to a back four, which saw the introduction of Jan Toral as well Meyler, was crucial.
Slutsky said: "David Meyler missed four months, he played in national team and each match was between two and three days and he is really not ready to play all games. We are waiting for him to reach optimum fitness and now it would be difficult for him to play each match.
“In one week no problem but three days very difficult, that’s why he played only 45 minutes and he changed the game.
“We played too defensive in the first half and it was terrible in the second half we played much better maybe the best quality of the match. Very difficult for me as some players missed pre-season and some just came here it makes it difficult for me to understand especially when you play over two days what is the best formation.”
Meyler himself said a point was a fair reflection of the game.
"After the second half we probably deserved a win, but in the first half Sunderland put us under a lot of pressure and were the better team so over 90 minutes 1-1 was probably a fair result," he said.
"They sat back a little bit in the second half and allowed us to get at them more, but that is only natural when you have a lead. We improved as well, though, after a few words at half time and we knew that it was on us to go back out there and challenge them.
"We had to take the game to them and we did. Sunderland were hard to break down and in this league, you know that every game you play is going to be tough. The first 45 minutes didn't go our way and we didn't do enough as a group but that is something we can have a look at and work on. The second half was an improvement but if we want to win games, we have to perform for 90 minutes. Only doing it for 45 minutes isn't good enough."