Chelsea had looked in a comfortable position when striker Tammy Abraham scored twice before half-time.

However, Callum Robinson pulled a goal back for the Blades with a close-range finish in the first minute of the second period.

French forward Lys Mousset, a 79th-minute substitute, then played a key role in earning United a surprise point when he connected with a Robinson cross and saw the ball deflect in off Zouma's shin.

Abraham opened the scoring as Chelsea made its superiority in the early stages of the game count.

United goalkeeper Dean Henderson, under pressure from Christian Pulisic, fumbled Abraham’s initial header from Cesar Azpilicueta’s high floating cross. Abraham was the quickest to react and from just outside the six-yard box he hooked the ball into the net on the half volley.

The Blades missed a great chance to equalise when Robinson's diving header from Chris Basham's cross went wide and Chelsea made them pay just before half-time as Abraham struck again.

Blades defenders Jack O'Connell and John Egan collided with each other as they challenged for the same ball, which allowed Abraham to break clear and crisply strike the ball past Henderson.

Robinson made up for his earlier miss when he pulled one back for the Blades almost immediately after the restart.

Enda Stevens got past Azpilicueta and delivered a teasing low cross into the box, which Robinson steered past Kepa Arrizabalaga.

Robinson then turned provider when his low cross was met by Mousset, who saw his effort go into the net off Zouma to deny Chelsea victory.

After the international break, Sheffield United hosts Southampton at Bramall Lane on 15 September (AEST). 

Chelsea is in league action on the same day with a difficult away trip to Wolverhampton Wanderers. Three days later it will welcome Spanish side Valencia to Stamford Bridge for its opening UEFA Champions League fixture.