Eintracht Frankfurt took the lead through their top scorer Luka Jovic as Pedro scored a crucial away goal for Chelsea as they recovered from an early setback in Germany.
The Blues go into the Europa League semi-final return leg at Stamford Bridge with an away goal advantage.
The Blues, who started with Eden Hazard on the bench, equalised when Pedro thrashed home just before half-time.
David Luiz also went close when his dipping free-kick came off the bar.
The second leg is on Thursday, 9 May.