Amid the jubilation that followed the final whistle at Stamford Bridge, where recovered from 2-0 down to progress as 6-3 winners in the Carabao Cup, it was easy to forget that Alonso's side were booed off at half-time.
Supporters witnessed arguably the worst first half of Alonso's short tenure to date, with fortunate not to be further in arrears after the head coach made nine changes to his line-up.
The team's rhythm was disrupted. made eight changes themselves, but Daniel Farke's side took control and were threatening to surge into the fourth round.
Defender Tarik Muharemovic opened the scoring before Brenden Aaronson doubled ' lead shortly after the break.
Alonso had responded to 's out-of-sorts start by making four substitutions at half-time. On came Cole Palmer, Morgan Rogers, Neto and Reece James, and together they changed the game.
The sight of Palmer and Rogers warming up had gladdened the hearts of many, turning jeers to cheers. By the end of the night, Palmer had scored twice, fellow substitute Pedro Neto had also found the net, and Rogers left the field after helping to create four goals from open play in 's remarkable turnaround.
However, speaking after the match, Alonso said he had made it "hard" for his players in the first place.
"I need to take my own blame and my own responsibility on the things that happen," he said. "I need to be able to help them better so they are not responsible, and after you need to react and think what's better for the team. "
Alonso said the raft of substitutions he felt compelled to make should be considered "part of the game".
However, only 35-year-old Danny Welbeck, who scored twice, emerged from the starters with a compelling case for more regular involvement.
Even Valentin Barco, despite scoring 's fifth goal, was partly at fault for ' second and was among several players who repeatedly surrendered possession during a difficult first half.
Young attackers Estevao Willian and Jamie Gittens suffered the disappointment of being substituted at half-time, while £40m signing Geovany Quenda, who joined from Sporting, did not add to his solitary substitute appearance for the club as he watched from the bench.
Midfielder Reggie Watson, making his debut at the age of 16, was also withdrawn at the break after being booked.
Alonso later said he would not take a "cynical" view as some on the outside might about the difference in level between his stars and 's back-up options.
He added: "I know that probably I have to take the right decisions for them to show their best level, so it's something that I will analyse and learn from today. "
Nevertheless, reaching the fourth round is important for .
It is not only about preserving their hopes of silverware in a season without European football, but are also a club that need as many competitive fixtures as possible.
They have a 27-man squad, supported by a strong academy pipeline, and these matches are vital for keeping a large group of players engaged throughout the campaign.
There is an irony, then, that Palmer, Rogers and 's other established stars may have secured future opportunities for the very fringe players whose performances had put the club's EFL Cup campaign at risk.