Title rivals Max Verstappen and Charles Leclerc will start the Belgian Grand Prix from the back of the grid.
The Red Bull and Ferrari stars are two of six drivers to be penalised for using too many engine parts, with McLaren’s Lando Norris another.
Verstappen, who leads Leclerc by 80 points in the championship, set the pace in Friday practice, an eye-opening 0.862secs quicker than Leclerc.
Norris was third, with Mercedes driver Lewis Hamilton in sixth.
The other drivers to have engine penalties are Alfa Romeo’s Valtteri Bottas, Alpine’s Esteban Ocon and Haas’ Mick Schumacher.
Verstappen’s pace looked hugely impressive and Leclerc certainly seemed to think it was an imposing time. When told of it by his engineer, Leclerc said: “Oh. 45.5 is quick.”
However, the size of the gap in a year when Ferrari and Red Bull have been so closely matched suggests that the cars may well not have been in comparable specification.
The race-simulation runs later in the session leant credence to that theory, although rain towards the end of the session cut them short.
Verstappen was quickest again on those – but only 0.3secs quicker than Sainz on average on the medium tyre. Leclerc did his long run on the soft tyre and was 0.3secs quicker than Mercedes’ George Russell, who was eighth fastest overall.
Despite the difficult conditions at the end of the sessions, no one crashed, although Hamilton had a scary moment when the car snapped through Eau Rouge and he ran off track collecting it.
Shortly afterwards, Schumacher went off at the Malmedy right-hander at the top of the hill, before the rain became heavy enough for the drivers to abandon running on slick tyres.