The Mexican's lobbed effort broke the deadlock just before the break, while Seferovic, making his debut for Sociedad following a summer move from Fiorentina, doubled the lead with 20 minutes remaining.
La Real went into the game with a host of key players missing - including last season's top scorer Imanol Agirretxe, - and coach Jagoba Arrasate, in his first game in charge of the club, also left Antoine Griezmann and captain Xabi Prieto on the bench, presumably with one eye on the Champions League play-off tie with Lyon next week.
Getafe showed early signs of ambition but the hosts were the first side to create real chances.
Gonzalo Castro was the first to trouble the Getafe defence, rattling the bar after a cross from Seferovic, and moments later the Swiss forward shot just over following a cross from Vela.
Ruben Pardo, who looks set to have a big season ahead of him after the departure of Asier Illarramendi to Real Madrid, also came close to scoring, chipping the ball inches over after he was set free by a pass from Seferovic.
Vela eventually gave Sociedad the lead they deserved, running onto a precise pass by Castro before chipping the ball over Miguel Angel Moya and into the net, giving his side the advantage as they headed to the dressing room at half-time.
Diego Castro was presented with Getafe's best chance midway through the second half, but skied his effort under pressure from Inigo Martinez.
Barely a minute later, Sociedad made sure of the points.
Seferovic raced behind the Getafe defence to meet a pass from Vela down the left-hand side and, in a similar fashion to Vela's opener, chipped the ball over the advancing Moya into the opposite corner.
The Basque side will now head into their game in Lyon in confident mood following the win, which will encourage their rookie coach Arrasate, who is looking to build on an excellent campaign last season which saw Sociedad finish fourth in La Liga under his predecessor Philippe Montanier.