The midfielder, on loan from Arsenal, continued his impressive goalscoring form after heading home from Jacob Murphy's cross on the stroke of half-time, becoming the first Newcastle player since Papiss Cissé in April 2012 to net in six successive Premier League games.
The Magpies, playing in front of a home crowd for the first time since February 2020, then held firm in the second-half to record a fifth league clean sheet of the season in their final home game of the 2020/21 campaign, despite David McGoldrick hitting the crossbar for the Blades.
Steve Bruce named an unchanged line-up from Friday's 4-3 defeat against Premier League champions Manchester City and faced a Sheffield United side targeting back-to-back league victories following a surprising 1-0 away win at Everton.
The visitors, rooted to the foot of the English top-flight, almost broke the deadlock inside the opening seven minutes as a dangerous attack saw Enda Stevens tee up McGoldrick but the Irish striker's side-footed effort flew narrowly wide of Dúbravka's left-hand post.
The Blades continued their push for an opener as neat build-up play between McGoldrick and Ben Osborn saw Jayden Bogle's inviting cross fizz across the six-yard area but the right-back's low pass was unable to find Daniel Jebbison inside the box.
Jonjo Shelvey went close to netting his second Premier League goal of the campaign as the midfielder rose high to meet Matt Ritchie's pinpoint cross from the left wing but the midfielder's header was superbly kept out by Blades goalkeeper Aaron Ramsdale before the loose ball was cleared to safety.
Federico Fernández then took his turn in front of goal but the Argentine's header, from Ritchie's bending corner, was comfortably held by the Blades shot-stopper.
With the half-time whistle approaching, Newcastle broke the deadlock in the fourth minute of additional time through Willock's accurate header.
After Allan Saint-Maximin evaded a group of Sheffield United defenders, the French winger threaded a neat pass towards Murphy before the right wing-back's floated cross from the byline fell kindly into Willock's path, who guided his effort home in front of a delighted Gallowgate End.
In the second-half, McGoldrick went close to drawing the Blades level as the striker's free-kick from the edge of the penalty area, was directed wide of the target.
Saint-Maximin went close to extending the Magpies' advantage towards the hour mark after racing onto Paul Dummett's lofted pass but the Frenchman was unable to net a third goal in as many games against Sheffield United as his strike, from a tight angle, was blocked by Ramsdale.
Willock and United's lead was almost doubled as the 21-year-old completed a fine solo run, shrugging off the challenge of two Blades defenders, but his fierce strike flew straight into the gloves of Ramsdale.
McGoldrick then struck the crossbar for Paul Heckingbottom's side as the former Republic of Ireland international's curling effort from distance clipped the woodwork.
Following Saint-Maximin and Willock's withdrawals through injury, United faced a late surge of attack from the West Yorkshire outfit but limited their opponents to a lack to clear-cut goalscoring opportunities to claim maximum points in front of 10,000 returning spectators.
Newcastle United: Martin Dúbravka, Jacob Murphy, Emil Krafth, Federico Fernández, Matt Ritchie, Jonjo Shelvey (c), Joe Willock (Andy Carroll 85), Miguel Almirón, Allan Saint-Maximin (Sean Longstaff 71), Joelinton (Dwight Gayle 46).
Subs not used: Mark Gillespie, Javier Manquillo, Ciaran Clark, Jamal Lewis, Matty Longstaff, Jeff Hendrick.
