Christopher Nkunku's penalty secured Enzo Maresca's first victory as Chelsea manager, giving the Blues a two-goal lead in their Conference League play-off first leg against Servette.
Chelsea, fielding a heavily rotated lineup, struggled to break through their Swiss opponents until Nkunku was brought down by goalkeeper Jeremy Frick early in the second half.
The French forward, one of only two players to retain their spot from the starting eleven that faced Manchester City in a 2-0 loss on Sunday, calmly converted the penalty to score the first goal of Maresca's tenure.
Nkunku, formerly of Paris Saint-Germain, celebrated in his signature style by pulling out a blue balloon, which he inflated in front of the ecstatic Chelsea supporters.
Chelsea nearly doubled their lead moments later when Frick hesitated on the ball, allowing 18-year-old Marc Guiu to pounce. However, the young Spanish forward lost his nerve, giving Frick just enough time to recover and make the save.
The Blues did eventually secure a second goal, with substitute Noni Madueke firing a powerful shot from a tight angle in the 72nd minute.
With a 2-0 advantage, Chelsea will feel confident heading into the second leg in Geneva on August 29, poised to advance to the group stage of European football's third-tier competition.
