The midfielder's sumptuous 67th-minute strike - his second goal in as many games - handed the Magpies a 1-0 win in front of a crowd of 52,264 at St James' Park and left them nine points clear of the Blues, one of their rivals for a top-six finish, having played a game more.
A deserved victory took Eddie Howe's side to 30 points for the campaign, a total they did not reach last season until March 10.
By contrast Chelsea, who had seen England goalkeeper Nick Pope claw away Conor Gallagher's goal-bound effort minutes earlier, headed home having suffered a third league defeat on the trot.
Armando Broja proved a real handful early on as he stretched the home defence with play switching quickly from end to end, but it was the home side who were first to threaten in earnest with 16 minutes gone when Willock tricked his way past Cesar Azpilicueta to cross to the far post.
Kalidou Koulibaly's header dropped to the in-form Miguel Almiron on the edge of the box, but the Paraguay international's volley was just too high.
The home side were working hard to press their opponents in possession with a particular focus on goalkeeper Edouard Mendy with the ball at his feet, but neither side was able to match enterprise with the required quality to ignite a largely-scrappy encounter.
That might have changed when Jorginho, Mason Mount and Lewis Hall combined to find Broja, but his shot on the turn was fielded comfortably by Pope.
Chelsea's focus on Magpies playmaker Bruno Guimaraes limited his influence on a congested midfield battle, although that created space in which Joelinton and Sean Longstaff began to prosper as the break approached.
The home side and their fans were appealing in vain for a penalty for handball against Trevoh Chalobah on the stroke of half-time after Longstaff's cross hit his arm as he slid in to block, and the whistle arrived with the deadlock unbroken.
Howe's men picked up where they had left off and went close within minutes of the restart when Kieran Trippier's cross opened the visitors up and Longstaff's shot was saved by Mendy before Mateo Kovacic blocked Guimaraes' follow-up.
Chelsea were relieved to see Willock's 56th-minute cross just elude Chris Wood as he slid in at the far post, but Fabian Schar had to block Kovacic's powerfully-struck shot and it took a superb flying save by Pope to keep out Gallagher's curled 65th-minute attempt.
The value of Pope's contribution increased significantly within two minutes when, after Almiron had cut across the edge of the penalty area, Willock stepped in to smash an unstoppable shot past Mendy and into the back of the net.
The visitors' response was concerted as they sought a way back into the contest, but Newcastle held firm amid a frenetic conclusion to secure the points.