Having stunned Barcelona in Spain last week – becoming the first side in five years to beat them on home soil – Chelsea were expecting a much-improved performance by the holders in the second leg.
It was still not the kind of scintillating Barcelona display we have become accustomed to but, with Bonmati pulling the strings and Caroline Graham Hansen finding space in behind, they piled pressure on the Chelsea defence early on.
However, the Blues acquitted themselves well and looked able to pose their own threat on the counter-attack when they won the ball back.
After Bonmati's opener, Chelsea finished the first half strongly and should have equalised on the night - but the unmarked Leupolz only managed to strike the bar after a pull back from Nusken in the box.
The second half proved to be a different story.
Not long after Nusken’s effort bounced off the far post, Buchanan was sent off for her second booking in quick succession and had to trudge down the tunnel.
Chelsea struggled to recover, particularly after Rolfo scored her 75th-minute penalty.
There were emotional scenes at full-time as Hayes, surrounded by her players on the pitch, looked close to tears having waved goodbye to Stamford Bridge for the final time.
Chelsea had dreamed of a fairytale quadruple to cap off their manager's 12-year tenure, but instead must focus solely on the defence of their Women's Super League title which is under threat from rivals Manchester City.
Barcelona will look to continue their European dominance and clinch a second successive continental crown in Bilbao on 25 May.