Michael Carrick’s suffered two early injury setbacks as both Emmanuel Latte Lath and Alex Bangura were forced inside 20 minutes.
The hosts took the lead eight minutes before half-time, though, with Hayden Hackney converting Isaiah Jones’ low cross. It means Boro will take a 1-0 lead into the second leg at Stamford Bridge later this month.
Here’s how each Middlesbrough player fared at the Riverside Stadium:
1. Tom Glover - 6
Was fortunate when he spilled a few shots from distance, especially one which dropped to Cole Palmer just before half-time, but kept a clean sheet to give Boro a first-leg lead. 6 Photo: George Wood
2. Rav van den Berg - 8
Started on the right of a back three and moved to right-back in a four after Bangura’s injury. Adapted well and got tight to Chelsea’s attacking players to prevent danger. 8 Photo: George Wood
3. Dael Fry - 8
Regularly positioned himself well in the heart of Boro’s defence to stop crosses and keep Chelsea’s expensive forward line out. A commanding display. 8 Photo: Ben Roberts Photo
4. Lukas Engel - 8
Defended well against Chelsea wideman Noni Madueke and was able to make a few forays forward from left-back. An impressive all-round display. 8 Photo: Catherine Ivill