Hazard and Isco have started just 10 Madrid games between them in all competitions this season and were again on the bench for Friday's (AEDT) Copa del Rey clash at Elche.
Isco was introduced late in normal time with the game goalless, before Hazard came on as the tie headed into extra time.
The pair did not have an immediate impact, as Marcelo was sent off and Gonzalo Verdu netted a deflected opener for Elche, but ultimately turned the match on its head.
Isco touched in an equaliser before Hazard's first goal of the season sent Madrid through.
A report last week claimed Madrid had accepted a bid from Newcastle United for Hazard, but it added the player rejected the move. He has now had two goal involvements in as many appearances – as many as in his previous 17.
A delighted Ancelotti appears convinced, saying of the winger and Isco: "I knew that changes could give a boost to the team and they have given it.
"[Hazard] and Isco have won the match. It has a meaning. It may be that they deserve to play more, but the past is the past and you have to look forward.
"I know that I can count on them and on a squad that has everything, an extraordinary character and that fights against adversity and never gives up.
"I'm very happy. I think it's the game that's given me the most happiness."
Both men might expect to feature again in the quarter-finals of the Copa in a fortnight, when Madrid will be without a host of South American stars due to a short international break outside of a FIFA window.
"Let's see if those who make the calendars wake up. It's nonsense," Ancelotti said of the issue. "It is inevitable, but it has to be changed. We have to make them fairer for everyone."
Madrid are playing in the last eight for the fifth time in six seasons, although they have not won the trophy since 2013-14. Only twice this century have the Blancos lifted the Copa.