The Germany international's second-half header was enough to earn the Blues a second win in nine Premier League games.
The makeshift striker nodded in Hakim Ziyech's cross in the 64th minute to bring some relief to under-fire manager Graham Potter, on the day the club announced the big-money arrival of Ukraine winger Mykhailo Mudryk from Shakhtar Donetsk.
The injury-hit Blues showed determination to dig in and grind out the result against Palace, with the players seemingly ready to fight for their manager as he attempts to steer the club through a transitional period and drag them up the table.
"That's a huge win for us, definitely," said Havertz. "The last few weeks have been tough for us. We knew that it wouldn't be easy today, we knew we'd have to work hard for the three points.
"But we said before the game that this could be a match that turns things around for us. I'm really happy to score and to help the team."
Potter was without 11 first-team players for Sunday's game at Stamford Bridge after Denis Zakaria's name was added to a lengthy injury list following last week's defeat to Fulham and new loan signing Joao Felix began a three-match ban for his red card at Craven Cottage.
There was some encouragement with the return of striker Pierre-Emerick Aubameyang from a back injury to play the final 30 minutes, but Potter expects to once again be working with reduced options for his side's trip to Liverpool on Saturday.
With Aubameyang having struggled for form since signing from Barcelona in the summer, that could mean Havertz - who missed two golden chances to add to his tally against the Eagles - again being pressed into duty as an emergency centre-forward.
"I have to give credit, it was a fantastic cross from (Ziyech) and even in the first half he put some good balls into me," Havertz said.
"It took a little while but I finally scored in the end and I'm really happy, especially because it helped us to a big three points.
"We got the three points and we can start moving forward now."