Mauricio Pochettino bemoaned Chelsea's profligacy following their shock 1-0 loss at Middlesbrough in the first leg of their Carabao Cup semi-final.
The Premier League side dominated at the Riverside Stadium but squandered a host of chances, with Cole Palmer particularly wasteful.
Hayden Hackney's first-half goal earned the Sky Bet Championship hosts a slender advantage ahead of the return meeting at Stamford Bridge in a fortnight's time.
'We had too many chances to score where we didn't score - that is football,' Blues boss Pochettino told Sky Sports.