Ipswich manager Mick McCarthy admitted it was a "painful way to go out" after a goal deep into extra time from Crawley striker Izale McLeod dumped his side out of the Capital One Cup.
Former MK Dons forward McLeod, who also got the winner in last Saturday's league opener at Barnsley, struck again from close in after Ipswich failed to clear a corner to seal a 1-0 win.
McCarthy, who gave debuts to four players and rested 10 first-teamers, said: "I would have preferred no extra time and it was a painful way to go out.
"The performance was okay in bits and we had chances to win the game but it's not good enough when you don't score.
"In the second half we let them off the hook a bit, but I was pleased with the youngsters and Matt Clarke, at left-back, had a super debut."
As well as 17-year-old Clarke, McCarthy gaves bows to Polish keeper Bartosz Bialkowski, central midfielder Kevin Bru and left-sided midfielder Alex Henshall.
He added: "Teddy Bishop, at 18, did well after coming off the bench and Darren McQueen also. That is encouraging for us to see these youngsters take their chance."
Crawley boss John Gregory paid tribute to his side's level of fitness after they became the ninth club from a lower division to dump Ipswich out of the competition in the last 12 years.
The former Aston Villa chief said: "It's a big scalp and we're all very happy.
"There was only one team in it during extra time. We played for 120 minutes and looked stronger than they did, we were dominating it physically."
Gregory admitted that Crawley had their slice of luck when striker Frank Nouble missed a clear opening after 15 minutes, while Red Devils keeper Brian Jensen brilliantly tipped a drive from Bishop onto the crossbar a minute from time.
Gregory added: "We won't be getting carried away, there's a lot more to come from us and we can pass better.
"We were lucky to be in the game after 15 minutes but my players never gave up and we showed a lot of passion.
"If we passed better I'd be happier but defensively we were very solid and resolute. We are in the next round and I'm very happy with the start we have made to the season."