Back in the starting lineup following his international exertions, Mount showcased an exquisite control and turn after collecting Jorginho’s low pass and expertly slotted past Agustin Marchesin from a tricky angle to give the Blues a half-time lead on neutral territory at Sevilla’s Ramon Sanchez Pizjuan Stadium - which will also play host to the second leg between the teams on April 13.
Three Lions team-mate Chilwell then popped up with the all-important second goal five minutes from time in Spain, catching Jesus Manuel Corona in possession before showing great composure to glide past another defender and then the goalkeeper, culminating in a calm finish into an empty net.
It was the perfect response from Chelsea to Saturday’s shock 5-2 Premier League home thrashing by relegation-threatened West Brom - their first defeat under Thomas Tuchel.
Antonio Rudiger started against Porto despite a training ground bust-up with goalkeeper Kepa Arrizabalaga that occured at Cobham in the aftermath of that shock loss on Sunday.
Chelsea certainly did not have things all their own way in Seville, with Mateus Uribe volleying over early on and Eduoard Mendy having to be alert to ensure that Otavio’s corner did not swerve in at the front post before Zaidu Sanusi blasted over from close range.
Mount scored with the Blues’ first shot of the game shortly after the half-hour mark, while Timo Werner headed an enticing cross from the England midfielder over the bar shortly after the interval.
Mendy then saved from Moussa Marega after some below-par Rudiger defending, while there were several important interventions from Chelsea captain Cesar Azpilicueta and Porto’s Luis Diaz whistled a shot narrowly wide of the far post.
The luckless Kai Havertz prodded wide from an offside position after Werner had squared a pass following Rudiger’s long-range shot and Mendy - also needed to deny Pepe - saved again from Marega, who later went down in the box under pressure from Azpilicueta, but saw penalty claims waved away by Slovenian referee Slavko Vincic.
Azpilicueta headed a great chance wide and Tuchel sent for Olivier Giroud and Christian Pulisic in place of the ineffective Havertz and Werner.
He also introduced Thiago Silva - fresh from his nightmare return from injury against West Brom - and the fit-again N’Golo Kante for the final 10 minutes, with Pulisic rattling the crossbar shortly before Chilwell’s crucial second goal.