Boro fought back a one-goal defect on two occasions, tying the game 2-2 in the final seconds of extra-time.
Goals from debutant Jordan Rossiter and Adam Reach took the game past the original 90 minutes, before Suso appeared to have won the game for the Reds. However, a clumsy foul by Kolo Toure brought down a second Chelsea loanee, Patrick Bamford, and he stepped up to convert his penalty - and take the game into a shoot-out.
What followed was a memorable event, with the 14-13 scoreline coming at the end of the longest penalty shoot-out in League Cup history.
Kenneth Omeruo played the entire game for Boro, and the Chelsea man was delighted with the commitment shown by both the team, and the fans who drove them on to grab a last-minute equaliser.
“It was a good game, everyone was fighting and it got to a stage where we gave everything. I think the support from the fans helped us a lot – they kept going even when we were losing and gave us a buzz.”
As the shoot-out circled the full starting line-up, Omeruo stepped up to take his spot-kick, but still managed to convert a powerfully struck effort despite having 120 minutes of intense action behind him.
“It [the game] took a lot out of everyone tonight, we’re exhausted,” said Kenneth.
“I didn’t even look at the goalkeeper when I took my penalty – I just went for power and hit it.
“The manager told us after the game how proud he is of us, and if we can play like this we will go up to the Premier League. But right now, we’re ready for Charlton on Saturday.”
Boro currently sit in fifth place in the Championship table, comfortably in the play-off places after eight games played.