Benfica will travel to Stamford Bridge for the return leg and will have a mountain to climb due as playing at the Bridge is tough. The one-goal deficit doesn't render things any easier for the Portuguese club.
The first leg showed a defensively resolute Chelsea that relied on efficient tactics, quick link-up play and counter-attacking football. It was not the greatest of matches by any means, but such a victory is crucial to a team whose morale has been down for a while now.
Here are eight things we learned from the first leg.