Wolves became the first Premier League club to win a Christmas Eve fixture since Leeds United's 3-1 victory over Manchester United in 1995.
"I had a call early this morning from the doctor. Jean Bellegarde not feeling well, Craig Dawson not being 100 percent from his virus," O'Neil said after Wolves extended their unbeaten run at home to six matches.
"We had to call up young lads to make sure they were available this morning... incredible win with what we had available to us, injuries and three young lads on the bench against a team and squad the size of Chelsea.
"To get every last bit out of everybody available, and for them to dig in and be together, and not scrap a win but to be comfortable for most of it, is huge credit to the group. I'll enjoy Christmas Day tomorrow after that."
Still injury woes linger as Dawson had to be replaced in the second half after he hurt himself while blocking Raheem Sterling's shot.
"It's a really deep cut on his knee," O'Neil said.
"He's all stitched up, every time he bends it hurts a little bit, but the physios and doctors assure me he'll be okay for the next game which is important to us."
Eleventh-placed Wolves will visit Brentford on Wednesday before hosting Everton on Saturday for their third game in six days.
