Chelsea broke their European away-day jinx to defeat FC Basel as Victor Moses and David Luiz handed the Blues a much-needed advantage ahead of the second leg.
In front of a bumper 36,000 crowd at St Jakob Park, Moses gave the visitors the lead from Frank Lampard's corner but Fabian Schar's late penalty looked like sharing the spoils.
But Luiz's stoppage time free-kick gave Rafa Benitez's side a significant advantage heading into the second at Stamford Bridge next week and helped Chelsea put on foot in next month's final in Amsterdam.
Despite the Swiss league leaders' unbeaten home record since the group stages it was Chelsea who looked the more composed side in the first half, with their defence boosted by the return on John Terry while Fernando Torres's troubles continued.
The Blues started the game lacking in possession, and Frank Lampard, who remains two goals away from the all-time Chelsea goalscoring record, denied after linking up with Eden Hazard for a shot at the net.
The subsequent corner evaded Branislav Ivanovic and was toe-poked goalwards by the incoming Moses, who netted his ninth goal of the season.
The Blues' lead evoked memories of Tottenham's lead in the quarter final second leg against Basel a fortnight ago, but while the Swiss giants fought back quickly on that occasion, they looked somewhat nervous in the final third, with Petr Cech only sporadically employed.
Terry appeared to take a knock towards the end of the first half, but the captain was up and defending again within minutes, and while Serey Die looked the most dangerous for Basel in the first half, the home side were unable to capitalise on their increasing pressure.
The second half saw more attacking bite from Basel, with Valentin Stocker hitting the woodwork early on. Torres also came close to scoring at the other end, coming out of his shell after a brilliant run from Hazard past three defenders before he found the floundering Spaniard.
Ashley Cole made the mistake of time wasting during a throw in, receiving a yellow card, which means he will now miss the second leg of the tie.
With the ball going from end to end, Basel began to regain control of possession, but Phillipp Degen's twisted knee proved disruptive.
Basel sprung into action after the defender was replaced, and within minutes were awarded a penalty after a clumsy challenge by Cesar Azpilicueta on Valentin Stocker. Cech was helpless to stop Schar's spot kick, despite getting his hands to the ball.
Chelsea immediately responded, but Torres went close once again but was unable to find the back of the net.
The final minutes continued to be end to end, but in the last seconds after Ramires was felled for a free-kick; Luiz duly converted as Chelsea grabbed a last-gasp win.