The magnificent Olivier Giroud scored all four goals as Chelsea cruised to a resounding Champions League win in Spain.
It ensured the Blues, whose place in the knockout stage was already assured, go through as group winners.
Giroud opened the scoring with a sublime finish after just eight minutes.
Kai Havertz surged towards the penalty area and set up the Frenchman, who worked the ball onto his left foot and steered his shot into the far corner of the net.
Chelsea would have gone further in front before half-time had Antonio Rudiger’s header from Emerson Palmieri’s left-wing corner not been brilliantly cleared off the line by Franco Vázquez.
The lead was doubled nine minutes into the second half.
Giroud finished in fine style again, collecting Mateo Kovacic’s pass and turning away from Sergi Gómez before calmly lifting the ball over keeper Alfonso Pastor.
Giroud completed his hat-trick by heading home N’Golo Kante’s right-wing cross.
And his fourth came from the penalty spot after he was bundled over by Gómez.
It was a great night for Chelsea, with Christian Pulisic back in the starting line-up after injury and Billy Gilmour returning to first-team action.
Youngster Gilmour, fit again after a knee injury, came on as a late substitute.
Chelsea: Mendy, Azpilicueta, Rudiger, Christensen, Emerson, Kovacic (Ziyech 67), Jorginho (Gilmour 85), Havertz (Kante 67), Hudson-Odoi, Giroud (Werner 85), Pulisic (Mount 67).
Subs not used: Kepa, Caballero, James, Tomori, Chilwell, Alonso, Abraham.
