Just 30 seconds into Jose Mourinho’s return, Manchester United trailed.
A long ball over the top from Marcos Alonso seemed ill-fated with three defenders surrounding Pedro, but Chris Smalling never collected himself and Pedro snuck through, snatching the ball and rounding David De Gea to put the Blues up almost immediately.
His goal is the fastest in the Premier League this season.
The game exploded open following the goal, with Manchester United looking for an equalizer almost straight away. Zlatan Ibrahimovic headed over and Marcus Rashford caused problems down the left inside the opening 10 minutes.