Chelsea moved six points clear at the top of the Premier League as Cesc Fabregas' first-half goal beat a stubborn Sunderland at the Stadium of Light.
Fabregas steered into the far corner from the edge of the box as the Blues recorded a 10th consecutive league victory.
Sunderland keeper Jordan Pickford saved from former Black Cat Marcos Alonso and Willian to prevent Chelsea from winning by a bigger margin.
The hosts, who had set up to try and nullify their opponent's attacking strength, had few chances although they could have snatched a point in injury time but Thibaut Courtois superbly denied Patrick van Aanholt.