Meanwhile, Real Betis hold a slender 2-1 advantage over Fiorentina in the other semi-final, setting up thrilling return legs.
Chelsea's dominance was evident early on, with Jadon Sancho opening the scoring in the 12th minute. The winger latched onto a lofted pass, slotted past the goalkeeper, and watched as Djurgarden's Marcus Danielson inadvertently turned the ball into his own net.
Noni Madueke doubled the lead just before half-time, cleverly deceiving the defence with a feint before firing a precise shot into the near post.
Djurgarden, hampered by a depleted squad of just 14 fit senior players, nearly pulled one back before the break, but Chelsea's Swedish-born goalkeeper Filip Jorgensen produced a stunning save to deny Tokmac Nguen's deflected effort.
Nicolas Jackson sealed Chelsea's grip on the tie after the interval, capitalising on a defensive error to tap in his first in the 59th minute, before unleashing a ferocious left-footed strike from the edge of the box six minutes later.
Djurgarden's 18-year-old debutant Isak Alemayehu Mulugeta offered a glimmer of hope with a powerful header for his first senior goal in the 68th minute, but Chelsea's lead remained formidable.
"We performed very well and took a big step towards the final, but we must stay focused," Jackson said post-match.
Chelsea's manager Enzo Maresca, reflecting on the result, cautioned against complacency. "It's a strong position, but we learned from our Legia Warsaw tie where we won 3-0 away and still faced challenges at home," he said, referencing Chelsea's only loss in the competition this season. A recent X post from Chelsea's official account echoed this sentiment, stating: "A great night in Sweden, but the job's not done. Focus on the second leg! #UECL"
Djurgarden, the first Swedish side to reach a European semi-final since 1987, face an uphill battle in the return leg. Their coach, Jani Honkavaara, acknowledged the challenge: "We fought with what we had, but Chelsea's quality was clear. We'll give everything in London."
In the parallel semi-final, Real Betis secured a 2-1 home win against Fiorentina. Abde Ezzalzouli's thunderous strike off the crossbar gave Betis an early lead, followed by Antony's stunning long-range effort in the 64th minute.
Fiorentina's Luca Ranieri pulled one back late on, keeping the tie alive. Betis' official X account celebrated the result, posting: "What a night at the VillamarÃn! 2-1 up, but we're ready for Florence! #HalaBetis"
Both ties remain open as Chelsea and Betis aim to secure their places in the final, set for May 28 in Wroclaw, Poland, where Chelsea could add to their illustrious European trophy cabinet. The second legs, scheduled for next Thursday, promise intense battles as Djurgarden and Fiorentina look to defy the odds.