Thiago Silva scored his first goal for Chelsea as they came from behind to emphatically extend their unbeaten run to 11 matches.
David McGoldrick gave Sheffield United an early lead at Stamford Bridge, where Tammy Abraham equalised and Ben Chilwell’s goal put Chelsea ahead 10 minutes before half-time.
Silva nodded in the third and Werner’s fine finished capped a resounding win.
McGoldrick’s opener was the first Premier League goal conceded by keeper Edouard Mendy since his move to west London.
Chelsea were caught out by a clever corner routine which resulted in McGoldrick diverting Sander Berge’s low shot into the net.
The hosts levelled when the recalled Mateo Kovacic was picked out by the outstanding Hakim Ziyech down the right and pulled the ball back for Abraham, whose shot bounced up off the ground and into the far corner.
Ziyech’s left-footed deliveries from the right flank were the key to Chelsea’s victory.
They led to Werner hitting the bar as well as goals for Chilwell and Silva.
Keeper Aaron Ramsdale parried the ball to Werner, whose first-time effort bounced off the woodwork.
And when the hapless Ramsdale failed to deal with another ball in from Ziyech, Chilwell bundled it in at the far post.
Ziyech was the provider again for Silva’s 77th-minute header.
And Werner took advantage of a fortunate ricochet three minutes later, firing home after finding himself in on goal.
Chelsea: Mendy, James, Silva, Zouma, Chilwell, Kante, Kovacic (Jorginho 71), Mount, Ziyech, Werner (Giroud 86), Abraham.
Subs not used: Caballero, Rudiger, Azpilicueta, Emerson, Hudson-Odoi.