Ziyech gave Chelsea the lead after N’Golo Kante won the ball in midfield, with Werner’s run opening up space for the winger to drive home with a superb strike.
He added another after the break, before Tottenham fought back with goals from Lucas Moura and Steven Bergwijn.
Ziyech also set up Werner to find the net – with the striker rounding new Spurs goalkeeper Pierluigi Gollini to fire into an empty net after being played in his team-mate.
As happened so often last season, the striker’s effort was ruled out for offside.
But replays showed the German international had timed his run perfectly, with no VAR available in pre-season to overturn the decision.
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